Curated collection of useful Javascript snippets that you can understand in 30 seconds or less.
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arrayGcdarrayLcmarrayMaxarrayMinchunkcompactcountOccurrencesdeepFlattendifferencedifferenceWithdistinctValuesOfArraydropElementsdropRighteveryNthfilterNonUniqueflattenflattenDepthgroupByheadinitialinitialize2DArrayinitializeArrayWithRangeinitializeArrayWithValuesintersectionlastmapObjectnthElementpickpullpullAtIndexpullAtValuequickSortremovesampleshufflesimilaritysymmetricDifferencetailtaketakeRightunionwithoutzipzipObject
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arrayAveragearraySumclampNumbercollatzdigitizedistancefactorialfibonaccifibonacciCountUntilNumfibonacciUntilNumgcdhammingDistanceinRangeisArmstrongNumberisDivisibleisEvenisPrimelcmmedianpalindromepercentilepowersetprimesrandomIntegerInRangerandomNumberInRangeroundstandardDeviation
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Given a key and a set of arguments, call them when given a context. Primarily useful in composition.
Use a closure to call a stored key with stored arguments.
const call = (key, ...args) => context => context[key](...args);Examples
Promise.resolve([1, 2, 3])
.then(call('map', x => 2 * x))
.then(console.log); //[ 2, 4, 6 ]
const map = call.bind(null, 'map');
Promise.resolve([1, 2, 3])
.then(map(x => 2 * x))
.then(console.log); //[ 2, 4, 6 ]Changes a function that accepts an array into a variadic function.
Given a function, return a closure that collects all inputs into an array-accepting function.
const collectInto = fn => (...args) => fn(args);Examples
const Pall = collectInto(Promise.all.bind(Promise));
let p1 = Promise.resolve(1);
let p2 = Promise.resolve(2);
let p3 = new Promise(resolve => setTimeout(resolve, 2000, 3));
Pall(p1, p2, p3).then(console.log);Flip takes a function as an argument, then makes the first argument the last
Return a closure that takes variadic inputs, and splices the last argument to make it the first argument before applying the rest.
const flip = fn => (...args) => fn(args.pop(), ...args);Examples
let a = { name: 'John Smith' };
let b = {};
const mergeFrom = flip(Object.assign);
let mergePerson = mergeFrom.bind(null, a);
mergePerson(b); // == b
b = {};
Object.assign(b, a); // == bPerforms left-to-right function composition.
Use Array.reduce() with the spread operator (...) to perform left-to-right function composition.
The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));Examples
const add5 = x => x + 5;
const multiply = (x, y) => x * y;
const multiplyAndAdd5 = pipeFunctions(multiply, add5);
multiplyAndAdd5(5, 2); // 15Converts an asynchronous function to return a promise.
Use currying to return a function returning a Promise that calls the original function.
Use the ...rest operator to pass in all the parameters.
In Node 8+, you can use util.promisify
const promisify = func => (...args) =>
new Promise((resolve, reject) =>
func(...args, (err, result) => (err ? reject(err) : resolve(result)))
);Examples
const delay = promisify((d, cb) => setTimeout(cb, d));
delay(2000).then(() => console.log('Hi!')); // // Promise resolves after 2sTakes a variadic function and returns a closure that accepts an array of arguments to map to the inputs of the function.
Use closures and the spread operator (...) to map the array of arguments to the inputs of the function.
const spreadOver = fn => argsArr => fn(...argsArr);Examples
const arrayMax = spreadOver(Math.max);
arrayMax([1, 2, 3]); // 3
arrayMax([1, 2, 4]); // 4Calculates the greatest common denominator (gcd) of an array of numbers.
Use Array.reduce() and the gcd formula (uses recursion) to calculate the greatest common denominator of an array of numbers.
const arrayGcd = arr => {
const gcd = (x, y) => (!y ? x : gcd(y, x % y));
return arr.reduce((a, b) => gcd(a, b));
};Examples
arrayGcd([1, 2, 3, 4, 5]); // 1
arrayGcd([4, 8, 12]); // 4Calculates the lowest common multiple (lcm) of an array of numbers.
Use Array.reduce() and the lcm formula (uses recursion) to calculate the lowest common multiple of an array of numbers.
const arrayLcm = arr => {
const gcd = (x, y) => (!y ? x : gcd(y, x % y));
const lcm = (x, y) => x * y / gcd(x, y);
return arr.reduce((a, b) => lcm(a, b));
};Examples
arrayLcm([1, 2, 3, 4, 5]); // 60
arrayLcm([4, 8, 12]); // 24Returns the maximum value in an array.
Use Math.max() combined with the spread operator (...) to get the maximum value in the array.
const arrayMax = arr => Math.max(...arr);Examples
arrayMax([10, 1, 5]); // 10Returns the minimum value in an array.
Use Math.min() combined with the spread operator (...) to get the minimum value in the array.
const arrayMin = arr => Math.min(...arr);Examples
arrayMin([10, 1, 5]); // 1Chunks an array into smaller arrays of a specified size.
Use Array.from() to create a new array, that fits the number of chunks that will be produced.
Use Array.slice() to map each element of the new array to a chunk the length of size.
If the original array can't be split evenly, the final chunk will contain the remaining elements.
const chunk = (arr, size) =>
Array.from({ length: Math.ceil(arr.length / size) }, (v, i) =>
arr.slice(i * size, i * size + size)
);Examples
chunk([1, 2, 3, 4, 5], 2); // [[1,2],[3,4],[5]]Removes falsey values from an array.
Use Array.filter() to filter out falsey values (false, null, 0, "", undefined, and NaN).
const compact = arr => arr.filter(Boolean);Examples
compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34]); // [ 1, 2, 3, 'a', 's', 34 ]Counts the occurrences of a value in an array.
Use Array.reduce() to increment a counter each time you encounter the specific value inside the array.
const countOccurrences = (arr, value) => arr.reduce((a, v) => (v === value ? a + 1 : a + 0), 0);Examples
countOccurrences([1, 1, 2, 1, 2, 3], 1); // 3Deep flattens an array.
Use recursion.
Use Array.concat() with an empty array ([]) and the spread operator (...) to flatten an array.
Recursively flatten each element that is an array.
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));Examples
deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]Returns the difference between two arrays.
Create a Set from b, then use Array.filter() on a to only keep values not contained in b.
const difference = (a, b) => {
const s = new Set(b);
return a.filter(x => !s.has(x));
};Examples
difference([1, 2, 3], [1, 2, 4]); // [3]Filters out all values from an array for which the comparator function does not return true.
Use Array.filter() and Array.find() to find the appropriate values.
const differenceWith = (arr, val, comp) => arr.filter(a => !val.find(b => comp(a, b)));Examples
differenceWith([1, 1.2, 1.5, 3], [1.9, 3], (a, b) => Math.round(a) == Math.round(b)); // [1, 1.2]Returns all the distinct values of an array.
Use ES6 Set and the ...rest operator to discard all duplicated values.
const distinctValuesOfArray = arr => [...new Set(arr)];Examples
distinctValuesOfArray([1, 2, 2, 3, 4, 4, 5]); // [1,2,3,4,5]Removes elements in an array until the passed function returns true. Returns the remaining elements in the array.
Loop through the array, using Array.slice() to drop the first element of the array until the returned value from the function is true.
Returns the remaining elements.
const dropElements = (arr, func) => {
while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1);
return arr;
};Examples
dropElements([1, 2, 3, 4], n => n >= 3); // [3,4]Returns a new array with n elements removed from the right.
Use Array.slice() to slice the remove the specified number of elements from the right.
const dropRight = (arr, n = 1) => arr.slice(0, -n);Examples
dropRight([1, 2, 3]); // [1,2]
dropRight([1, 2, 3], 2); // [1]
dropRight([1, 2, 3], 42); // []Returns every nth element in an array.
Use Array.filter() to create a new array that contains every nth element of a given array.
const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === nth - 1);Examples
everyNth([1, 2, 3, 4, 5, 6], 2); // [ 2, 4, 6 ]Filters out the non-unique values in an array.
Use Array.filter() for an array containing only the unique values.
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));Examples
filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1,3,5]Flattens an array.
Use a new array and concatenate it with the spread input array causing a shallow denesting of any contained arrays.
const flatten = arr => [].concat(...arr);Examples
flatten([1, [2], 3, 4]); // [1,2,3,4]Flattens an array up to the specified depth.
Use recursion, decrementing depth by 1 for each level of depth.
Use Array.reduce() and Array.concat() to merge elements or arrays.
Base case, for depth equal to 1 stops recursion.
Omit the second element, depth to flatten only to a depth of 1 (single flatten).
const flattenDepth = (arr, depth = 1) =>
depth != 1
? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flattenDepth(v, depth - 1) : v), [])
: arr.reduce((a, v) => a.concat(v), []);Examples
flattenDepth([1, [2], 3, 4]); // [1,2,3,4]Groups the elements of an array based on the given function.
Use Array.map() to map the values of an array to a function or property name.
Use Array.reduce() to create an object, where the keys are produced from the mapped results.
const groupBy = (arr, func) =>
arr.map(typeof func === 'function' ? func : val => val[func]).reduce((acc, val, i) => {
acc[val] = (acc[val] || []).concat(arr[i]);
return acc;
}, {});Examples
groupBy([6.1, 4.2, 6.3], Math.floor); // {4: [4.2], 6: [6.1, 6.3]}
groupBy(['one', 'two', 'three'], 'length'); // {3: ['one', 'two'], 5: ['three']}Returns the head of a list.
Use arr[0] to return the first element of the passed array.
const head = arr => arr[0];Examples
head([1, 2, 3]); // 1Returns all the elements of an array except the last one.
Use arr.slice(0,-1) to return all but the last element of the array.
const initial = arr => arr.slice(0, -1);Examples
initial([1, 2, 3]); // [1,2]Initializes a 2D array of given width and height and value.
Use Array.map() to generate h rows where each is a new array of size w initialize with value. If the value is not provided, default to null.
const initialize2DArray = (w, h, val = null) =>
Array(h)
.fill()
.map(() => Array(w).fill(val));Examples
initialize2DArray(2, 2, 0); // [[0,0], [0,0]]Initializes an array containing the numbers in the specified range where start and end are inclusive.
Use Array((end + 1) - start) to create an array of the desired length, Array.map() to fill with the desired values in a range.
You can omit start to use a default value of 0.
const initializeArrayWithRange = (end, start = 0) =>
Array.from({ length: end + 1 - start }).map((v, i) => i + start);Examples
initializeArrayWithRange(5); // [0,1,2,3,4,5]
initializeArrayWithRange(7, 3); // [3,4,5,6,7]Initializes and fills an array with the specified values.
Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values.
You can omit value to use a default value of 0.
const initializeArrayWithValues = (n, value = 0) => Array(n).fill(value);Examples
initializeArrayWithValues(5, 2); // [2,2,2,2,2]Returns a list of elements that exist in both arrays.
Create a Set from b, then use Array.filter() on a to only keep values contained in b.
const intersection = (a, b) => {
const s = new Set(b);
return a.filter(x => s.has(x));
};Examples
intersection([1, 2, 3], [4, 3, 2]); // [2,3]Returns the last element in an array.
Use arr.length - 1 to compute the index of the last element of the given array and returning it.
const last = arr => arr[arr.length - 1];Examples
last([1, 2, 3]); // 3Maps the values of an array to an object using a function, where the key-value pairs consist of the original value as the key and the mapped value.
Use an anonymous inner function scope to declare an undefined memory space, using closures to store a return value. Use a new Array to store the array with a map of the function over its data set and a comma operator to return a second step, without needing to move from one context to another (due to closures and order of operations).
const mapObject = (arr, fn) =>
(a => (
(a = [arr, arr.map(fn)]), a[0].reduce((acc, val, ind) => ((acc[val] = a[1][ind]), acc), {})
))();Examples
const squareIt = arr => mapObject(arr, a => a * a);
squareIt([1, 2, 3]); // { 1: 1, 2: 4, 3: 9 }Returns the nth element of an array.
Use Array.slice() to get an array containing the nth element at the first place.
If the index is out of bounds, return [].
Omit the second argument, n, to get the first element of the array.
const nthElement = (arr, n = 0) => (n > 0 ? arr.slice(n, n + 1) : arr.slice(n))[0];Examples
nthElement(['a', 'b', 'c'], 1); // 'b'
nthElement(['a', 'b', 'b'], -3); // 'a'Picks the key-value pairs corresponding to the given keys from an object.
Use Array.reduce() to convert the filtered/picked keys back to an object with the corresponding key-value pair if the key exists in the obj.
const pick = (obj, arr) =>
arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});Examples
pick({ a: 1, b: '2', c: 3 }, ['a', 'c']); // { 'a': 1, 'c': 3 }Mutates the original array to filter out the values specified.
Use Array.filter() and Array.includes() to pull out the values that are not needed.
Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
(For a snippet that does not mutate the original array see without)
const pull = (arr, ...args) => {
let argState = Array.isArray(args[0]) ? args[0] : args;
let pulled = arr.filter((v, i) => !argState.includes(v));
arr.length = 0;
pulled.forEach(v => arr.push(v));
};Examples
let myArray1 = ['a', 'b', 'c', 'a', 'b', 'c'];
pull(myArray1, 'a', 'c');
console.log(myArray1); // [ 'b', 'b' ]
let myArray2 = ['a', 'b', 'c', 'a', 'b', 'c'];
pull(myArray2, ['a', 'c']);
console.log(myArray2); // [ 'b', 'b' ]Mutates the original array to filter out the values at the specified indexes.
Use Array.filter() and Array.includes() to pull out the values that are not needed.
Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
Use Array.push() to keep track of pulled values
const pullAtIndex = (arr, pullArr) => {
let removed = [];
let pulled = arr
.map((v, i) => (pullArr.includes(i) ? removed.push(v) : v))
.filter((v, i) => !pullArr.includes(i));
arr.length = 0;
pulled.forEach(v => arr.push(v));
return removed;
};Examples
let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtIndex(myArray, [1, 3]);
console.log(myArray); // [ 'a', 'c' ]
console.log(pulled); // [ 'b', 'd' ]Mutates the original array to filter out the values specified. Returns the removed elements.
Use Array.filter() and Array.includes() to pull out the values that are not needed.
Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
Use Array.push() to keep track of pulled values
const pullAtValue = (arr, pullArr) => {
let removed = [],
pushToRemove = arr.forEach((v, i) => (pullArr.includes(v) ? removed.push(v) : v)),
mutateTo = arr.filter((v, i) => !pullArr.includes(v));
arr.length = 0;
mutateTo.forEach(v => arr.push(v));
return removed;
};Examples
let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtValue(myArray, ['b', 'd']);
console.log(myArray); // [ 'a', 'c' ]
console.log(pulled); // [ 'b', 'd' ]QuickSort an Array (ascending sort by default).
Use recursion.
Use Array.filter and spread operator (...) to create an array that all elements with values less than the pivot come before the pivot, and all elements with values greater than the pivot come after it.
If the parameter desc is truthy, return array sorts in descending order.
const quickSort = ([n, ...nums], desc) =>
isNaN(n)
? []
: [
...quickSort(nums.filter(v => (desc ? v > n : v <= n)), desc),
n,
...quickSort(nums.filter(v => (!desc ? v > n : v <= n)), desc)
];Examples
quickSort([4, 1, 3, 2]); // [1,2,3,4]
quickSort([4, 1, 3, 2], true); // [4,3,2,1]Removes elements from an array for which the given function returns false.
Use Array.filter() to find array elements that return truthy values and Array.reduce() to remove elements using Array.splice().
The func is invoked with three arguments (value, index, array).
const remove = (arr, func) =>
Array.isArray(arr)
? arr.filter(func).reduce((acc, val) => {
arr.splice(arr.indexOf(val), 1);
return acc.concat(val);
}, [])
: [];Examples
remove([1, 2, 3, 4], n => n % 2 == 0); // [2, 4]Returns a random element from an array.
Use Math.random() to generate a random number, multiply it by length and round it of to the nearest whole number using Math.floor().
This method also works with strings.
const sample = arr => arr[Math.floor(Math.random() * arr.length)];Examples
sample([3, 7, 9, 11]); // 9Randomizes the order of the values of an array, returning a new array.
Uses the Fisher-Yates algoritm to reorder the elements of the array, based on the Lodash implementation, but as a pure function.
const shuffle = ([...arr]) => {
let m = arr.length;
while (m) {
const i = Math.floor(Math.random() * m--);
[arr[m], arr[i]] = [arr[i], arr[m]];
}
return arr;
};Examples
const foo = [1, 2, 3];
shuffle(foo); // [2,3,1]
console.log(foo); // [1,2,3]Returns an array of elements that appear in both arrays.
Use filter() to remove values that are not part of values, determined using includes().
const similarity = (arr, values) => arr.filter(v => values.includes(v));Examples
similarity([1, 2, 3], [1, 2, 4]); // [1,2]Returns the symmetric difference between two arrays.
Create a Set from each array, then use Array.filter() on each of them to only keep values not contained in the other.
const symmetricDifference = (a, b) => {
const sA = new Set(a),
sB = new Set(b);
return [...a.filter(x => !sB.has(x)), ...b.filter(x => !sA.has(x))];
};Examples
symmetricDifference([1, 2, 3], [1, 2, 4]); // [3,4]Returns all elements in an array except for the first one.
Return arr.slice(1) if the array's length is more than 1, otherwise, return the whole array.
const tail = arr => (arr.length > 1 ? arr.slice(1) : arr);Examples
tail([1, 2, 3]); // [2,3]
tail([1]); // [1]Returns an array with n elements removed from the beginning.
Use Array.slice() to create a slice of the array with n elements taken from the beginning.
const take = (arr, n = 1) => arr.slice(0, n);Examples
take([1, 2, 3], 5); // [1, 2, 3]
take([1, 2, 3], 0); // []Returns an array with n elements removed from the end.
Use Array.slice() to create a slice of the array with n elements taken from the end.
const takeRight = (arr, n = 1) => arr.slice(arr.length - n, arr.length);Examples
takeRight([1, 2, 3], 2); // [ 2, 3 ]
takeRight([1, 2, 3]); // [3]Returns every element that exists in any of the two arrays once.
Create a Set with all values of a and b and convert to an array.
const union = (a, b) => Array.from(new Set([...a, ...b]));Examples
union([1, 2, 3], [4, 3, 2]); // [1,2,3,4]Filters out the elements of an array, that have one of the specified values.
Use Array.filter() to create an array excluding(using !Array.includes()) all given values.
(For a snippet that mutates the original array see pull)
const without = (arr, ...args) => arr.filter(v => !args.includes(v));Examples
without([2, 1, 2, 3], 1, 2); // [3]Creates an array of elements, grouped based on the position in the original arrays.
Use Math.max.apply() to get the longest array in the arguments.
Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements.
If lengths of the argument-arrays vary, undefined is used where no value could be found.
const zip = (...arrays) => {
const maxLength = Math.max(...arrays.map(x => x.length));
return Array.from({ length: maxLength }).map((_, i) => {
return Array.from({ length: arrays.length }, (_, k) => arrays[k][i]);
});
};Examples
zip(['a', 'b'], [1, 2], [true, false]); // [['a', 1, true], ['b', 2, false]]
zip(['a'], [1, 2], [true, false]); // [['a', 1, true], [undefined, 2, false]]Given an array of valid property identifiers and an array of values, return an object associating the properties to the values.
Since an object can have undefined values but not undefined property pointers, the array of properties is used to decide the structure of the resulting object using Array.reduce().
const zipObject = (props, values) =>
props.reduce((obj, prop, index) => ((obj[prop] = values[index]), obj), {});Examples
zipObject(['a', 'b', 'c'], [1, 2]); // {a: 1, b: 2, c: undefined}
zipObject(['a', 'b'], [1, 2, 3]); // {a: 1, b: 2}Converts the given array elements into <li> tags and appends them to the list of the given id.
Use Array.map() and document.querySelector() to create a list of html tags.
const arrayToHtmlList = (arr, listID) =>
arr.map(item => (document.querySelector('#' + listID).innerHTML += `<li>${item}</li>`));Examples
arrayToHtmlList(['item 1', 'item 2'], 'myListID');Returns true if the bottom of the page is visible, false otherwise.
Use scrollY, scrollHeight and clientHeight to determine if the bottom of the page is visible.
const bottomVisible = () =>
document.documentElement.clientHeight + window.scrollY >=
(document.documentElement.scrollHeight || document.documentElement.clientHeight);Examples
bottomVisible(); // trueReturns the current URL.
Use window.location.href to get current URL.
const currentURL = () => window.location.href;Examples
currentURL(); // 'https://google.com'Detects wether the website is being opened in a mobile device or a desktop/laptop.
Use a regular expression to test the navigator.userAgent property to figure out if the device is a mobile device or a desktop/laptop.
const detectDeviceType = () =>
/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
? 'Mobile'
: 'Desktop';Examples
detectDeviceType(); // "Mobile"
detectDeviceType(); // "Desktop"Returns true if the element specified is visible in the viewport, false otherwise.
Use Element.getBoundingClientRect() and the window.inner(Width|Height) values
to determine if a given element is visible in the viewport.
Omit the second argument to determine if the element is entirely visible, or specify true to determine if
it is partially visible.
const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
const { top, left, bottom, right } = el.getBoundingClientRect();
const { innerHeight, innerWidth } = window;
return partiallyVisible
? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
: top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};Examples
// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
elementIsVisibleInViewport(el); // false // (not fully visible)
elementIsVisibleInViewport(el, true); // true // (partially visible)Returns the scroll position of the current page.
Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and scrollTop.
You can omit el to use a default value of window.
const getScrollPosition = (el = window) => ({
x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});Examples
getScrollPosition(); // {x: 0, y: 200}Returns the value of a CSS rule for the specified element.
Use Window.getComputedStyle() to get the value of the CSS rule for the specified element.
const getStyle = (el, ruleName) => getComputedStyle(el)[ruleName];Examples
getStyle(document.querySelector('p'), 'font-size'); // '16px'Returns an object containing the parameters of the current URL.
Use match() with an appropriate regular expression to get all key-value pairs, Array.reduce() to map and combine them into a single object.
Pass location.search as the argument to apply to the current url.
const getURLParameters = url =>
url
.match(/([^?=&]+)(=([^&]*))/g)
.reduce((a, v) => ((a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a), {});Examples
getURLParameters('http://url.com/page?name=Adam&surname=Smith'); // {name: 'Adam', surname: 'Smith'}Returns true if the element has the specified class, false otherwise.
Use element.classList.contains() to check if the element has the specified class.
const hasClass = (el, className) => el.classList.contains(className);Examples
hasClass(document.querySelector('p.special'), 'special'); // trueHides all the elements specified.
Use the spread operator (...) and Array.forEach() to apply display: none to each element specified.
const hide = (...el) => [...el].forEach(e => (e.style.display = 'none'));Examples
hide(document.querySelectorAll('img')); // Hides all <img> elements on the pageRedirects the page to HTTPS if its currently in HTTP. Also, pressing the back button doesn't take it back to the HTTP page as its replaced in the history.
Use location.protocol to get the protocol currently being used. If it's not HTTPS, use location.replace() to replace the existing page with the HTTPS version of the page. Use location.href to get the full address, split it with String.split() and remove the protocol part of the URL.
Examples
const httpsRedirect = () => {
if (location.protocol !== 'https:') location.replace('https://' + location.href.split('//')[1]);
};Redirects to a specified URL.
Use window.location.href or window.location.replace() to redirect to url.
Pass a second argument to simulate a link click (true - default) or an HTTP redirect (false).
const redirect = (url, asLink = true) =>
asLink ? (window.location.href = url) : window.location.replace(url);Examples
redirect('https://google.com');Smooth-scrolls to the top of the page.
Get distance from top using document.documentElement.scrollTop or document.body.scrollTop.
Scroll by a fraction of the distance from the top. Use window.requestAnimationFrame() to animate the scrolling.
const scrollToTop = () => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if (c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c / 8);
}
};Examples
scrollToTop();Sets the value of a CSS rule for the specified element.
Use element.style to set the value of the CSS rule for the specified element to value.
const setStyle = (el, ruleName, value) => (el.style[ruleName] = value);Examples
setStyle(document.querySelector('p'), 'font-size', '20px'); // The first <p> element on the page will have a font-size of 20pxShows all the elements specified.
Use the spread operator (...) and Array.forEach() to clear the display property for each element specified.
const show = (...el) => [...el].forEach(e => (e.style.display = ''));Examples
show(document.querySelectorAll('img')); // Shows all <img> elements on the pageToggle a class for an element.
Use element.classList.toggle() to toggle the specified class for the element.
const toggleClass = (el, className) => el.classList.toggle(className);Examples
toggleClass(document.querySelector('p.special'), 'special'); // The paragraph will not have the 'special' class anymoreReturns the difference (in days) between two dates.
Calculate the difference (in days) between two Date objects.
const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
(dateFinal - dateInitial) / (1000 * 3600 * 24);Examples
getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9Converts a JSON object to a date.
Use Date(), to convert dates in JSON format to readable format (dd/mm/yyyy).
const JSONToDate = arr => {
const dt = new Date(parseInt(arr.toString().substr(6)));
return `${dt.getDate()}/${dt.getMonth() + 1}/${dt.getFullYear()}`;
};Examples
JSONToDate(/Date(1489525200000)/); // "14/3/2017"Converts a date from American format to English format.
Use Date.toISOString(), split('T') and replace() to convert a date from American format to the English format.
Throws an error if the passed time cannot be converted to a date.
const toEnglishDate = time => {
try {
return new Date(time)
.toISOString()
.split('T')[0]
.replace(/-/g, '/');
} catch (e) {}
};Examples
toEnglishDate('09/21/2010'); // '21/09/2010'Results in a string representation of tomorrow's date.
Use new Date() to get today's date, adding 86400000 of seconds to it(24 hours), using toISOString to convert Date object to string.
const tomorrow = () => new Date(new Date().getTime() + 86400000).toISOString().split('T')[0];Examples
tomorrow(); // 2017-12-27 (if current date is 2017-12-26)Chains asynchronous functions.
Loop through an array of functions containing asynchronous events, calling next when each asynchronous event has completed.
const chainAsync = fns => {
let curr = 0;
const next = () => fns[curr++](next);
next();
};Examples
chainAsync([
next => {
console.log('0 seconds');
setTimeout(next, 1000);
},
next => {
console.log('1 second');
setTimeout(next, 1000);
},
next => {
console.log('2 seconds');
}
]);Performs right-to-left function composition.
Use Array.reduce() to perform right-to-left function composition.
The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.
const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args)));Examples
const add5 = x => x + 5;
const multiply = (x, y) => x * y;
const multiplyAndAdd5 = compose(add5, multiply);
multiplyAndAdd5(5, 2); // 15Curries a function.
Use recursion.
If the number of provided arguments (args) is sufficient, call the passed function fn.
Otherwise, return a curried function fn that expects the rest of the arguments.
If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. Math.min()), you can optionally pass the number of arguments to the second parameter arity.
const curry = (fn, arity = fn.length, ...args) =>
arity <= args.length ? fn(...args) : curry.bind(null, fn, arity, ...args);Examples
curry(Math.pow)(2)(10); // 1024
curry(Math.min, 3)(10)(50)(2); // 2Logs the name of a function.
Use console.debug() and the name property of the passed method to log the method's name to the debug channel of the console.
const functionName = fn => (console.debug(fn.name), fn);Examples
functionName(Math.max); // max (logged in debug channel of console)Runs an array of promises in series.
Use Array.reduce() to create a promise chain, where each promise returns the next promise when resolved.
const runPromisesInSeries = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());Examples
const delay = d => new Promise(r => setTimeout(r, d));
runPromisesInSeries([() => delay(1000), () => delay(2000)]); // //executes each promise sequentially, taking a total of 3 seconds to completeDelays the execution of an asynchronous function.
Delay executing part of an async function, by putting it to sleep, returning a Promise.
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));Examples
async function sleepyWork() {
console.log("I'm going to sleep for 1 second.");
await sleep(1000);
console.log('I woke up after 1 second.');
}Negates a predicate function.
Take a predicate function and apply not to it with its arguments.
const negate = func => (...args) => !func(...args);Examples
filter([1, 2, 3, 4, 5, 6], negate(isEven)); // [1, 3, 5]
negate(isOdd)(1); // falseReturns the average of an array of numbers.
Use Array.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
const arrayAverage = arr => arr.reduce((acc, val) => acc + val, 0) / arr.length;Examples
arrayAverage([1, 2, 3]); // 2Returns the sum of an array of numbers.
Use Array.reduce() to add each value to an accumulator, initialized with a value of 0.
const arraySum = arr => arr.reduce((acc, val) => acc + val, 0);Examples
arraySum([1, 2, 3, 4]); // 10Clamps num within the inclusive range specified by the boundary values a and b.
If num falls within the range, return num.
Otherwise, return the nearest number in the range.
const clampNumber = (num, a, b) => Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b));Examples
clampNumber(2, 3, 5); // 3
clampNumber(1, -1, -5); // -1
clampNumber(3, 2, 4); // 3Applies the Collatz algorithm.
If n is even, return n/2. Otherwise, return 3n+1.
const collatz = n => (n % 2 == 0 ? n / 2 : 3 * n + 1);Examples
collatz(8); // 4
collatz(5); // 16Converts a number to an array of digits.
Convert the number to a string, using spread operators in ES6([...string]) build an array.
Use Array.map() and parseInt() to transform each value to an integer.
const digitize = n => [...('' + n)].map(i => parseInt(i));Examples
digitize(123); // [1, 2, 3]Returns the distance between two points.
Use Math.hypot() to calculate the Euclidean distance between two points.
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);Examples
distance(1, 1, 2, 3); // 2.23606797749979Calculates the factorial of a number.
Use recursion.
If n is less than or equal to 1, return 1.
Otherwise, return the product of n and the factorial of n - 1.
Throws an exception if n is a negative number.
const factorial = n =>
n < 0
? (() => {
throw new TypeError('Negative numbers are not allowed!');
})()
: n <= 1 ? 1 : n * factorial(n - 1);Examples
factorial(6); // 720Generates an array, containing the Fibonacci sequence, up until the nth term.
Create an empty array of the specific length, initializing the first two values (0 and 1).
Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two.
const fibonacci = n =>
Array.from({ length: n }).reduce(
(acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i),
[]
);Examples
fibonacci(6); // 720Returns the number of fibonnacci numbers up to num(0 and num inclusive).
Use a mathematical formula to calculate the number of fibonacci numbers until num.
const fibonacciCountUntilNum = num =>
Math.ceil(Math.log(num * Math.sqrt(5) + 1 / 2) / Math.log((Math.sqrt(5) + 1) / 2));Examples
fibonacciCountUntilNum(10); // 7Generates an array, containing the Fibonacci sequence, up until the nth term.
Create an empty array of the specific length, initializing the first two values (0 and 1).
Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two.
Uses a mathematical formula to calculate the length of the array required.
const fibonacciUntilNum = num => {
let n = Math.ceil(Math.log(num * Math.sqrt(5) + 1 / 2) / Math.log((Math.sqrt(5) + 1) / 2));
return Array.from({ length: n }).reduce(
(acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i),
[]
);
};Examples
fibonacciCountUntilNum(10); // 7Calculates the greatest common divisor between two numbers.
Use recursion.
Base case is when y equals 0. In this case, return x.
Otherwise, return the GCD of y and the remainder of the division x/y.
const gcd = (x, y) => (!y ? x : gcd(y, x % y));Examples
gcd(8, 36); // 4Calculates the Hamming distance between two values.
Use XOR operator (^) to find the bit difference between the two numbers, convert to a binary string using toString(2).
Count and return the number of 1s in the string, using match(/1/g).
const hammingDistance = (num1, num2) => ((num1 ^ num2).toString(2).match(/1/g) || '').length;Examples
hammingDistance(2, 3); // 1Checks if the given number falls within the given range.
Use arithmetic comparison to check if the given number is in the specified range.
If the second parameter, end, is not specified, the range is considered to be from 0 to start.
const inRange = (n, start, end = null) => {
if (end && start > end) end = [start, (start = end)][0];
return end == null ? n >= 0 && n < start : n >= start && n < end;
};Examples
inRange(3, 2, 5); // true
inRange(3, 4); // true
inRange(2, 3, 5); // false
inrange(3, 2); // falseChecks if the given number is an Armstrong number or not.
Convert the given number into an array of digits. Use Math.pow() to get the appropriate power for each digit and sum them up. If the sum is equal to the number itself, return true otherwise false.
const isArmstrongNumber = digits =>
(arr => arr.reduce((a, d) => a + Math.pow(parseInt(d), arr.length), 0) == digits)(
(digits + '').split('')
);Examples
isArmstrongNumber(1634); // true
isArmstrongNumber(371); // true
isArmstrongNumber(56); // falseChecks if the first numeric argument is divisible by the second one.
Use the modulo operator (%) to check if the remainder is equal to 0.
const isDivisible = (dividend, divisor) => dividend % divisor === 0;Examples
isDivisible(6, 3); // trueReturns true if the given number is even, false otherwise.
Checks whether a number is odd or even using the modulo (%) operator.
Returns true if the number is even, false if the number is odd.
const isEven = num => num % 2 === 0;Examples
isEven(3); // falseChecks if the provided integer is a prime number.
Check numbers from 2 to the square root of the given number.
Return false if any of them divides the given number, else return true, unless the number is less than 2.
const isPrime = num => {
const boundary = Math.floor(Math.sqrt(num));
for (var i = 2; i * i <= boundary; i++) if (num % i == 0) return false;
return num >= 2;
};Examples
isPrime(11); // true
isPrime(12); // falseReturns the least common multiple of two numbers.
Use the greatest common divisor (GCD) formula and Math.abs() to determine the least common multiple.
The GCD formula uses recursion.
const lcm = (x, y) => {
const gcd = (x, y) => (!y ? x : gcd(y, x % y));
return Math.abs(x * y) / gcd(x, y);
};Examples
lcm(12, 7); // 84Returns the median of an array of numbers.
Find the middle of the array, use Array.sort() to sort the values.
Return the number at the midpoint if length is odd, otherwise the average of the two middle numbers.
const median = arr => {
const mid = Math.floor(arr.length / 2),
nums = [...arr].sort((a, b) => a - b);
return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
};Examples
median([5, 6, 50, 1, -5]); // 5
median([0, 10, -2, 7]); // 3.5Returns true if the given string is a palindrome, false otherwise.
Convert string toLowerCase() and use replace() to remove non-alphanumeric characters from it.
Then, split('') into individual characters, reverse(), join('') and compare to the original, unreversed string, after converting it tolowerCase().
const palindrome = str => {
const s = str.toLowerCase().replace(/[\W_]/g, '');
return (
s ===
s
.split('')
.reverse()
.join('')
);
};Examples
palindrome('taco cat'); // trueUses the percentile formula to calculate how many numbers in the given array are less or equal to the given value.
Use Array.reduce() to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.
const percentile = (arr, val) =>
100 * arr.reduce((acc, v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;Examples
percentile([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 6); // 55Returns the powerset of a given array of numbers.
Use Array.reduce() combined with Array.map() to iterate over elements and combine into an array containing all combinations.
const powerset = arr => arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]);Examples
powerset([1, 2]); // [[], [1], [2], [2,1]]Generates primes up to a given number, using the Sieve of Eratosthenes.
Generate an array from 2 to the given number. Use Array.filter() to filter out the values divisible by any number from 2 to the square root of the provided number.
const primes = num => {
let arr = Array.from({ length: num - 1 }).map((x, i) => i + 2),
sqroot = Math.floor(Math.sqrt(num)),
numsTillSqroot = Array.from({ length: sqroot - 1 }).map((x, i) => i + 2);
numsTillSqroot.forEach(x => (arr = arr.filter(y => y % x !== 0 || y == x)));
return arr;
};Examples
primes(10); // [2,3,5,7]Returns a random integer in the specified range.
Use Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.
const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;Examples
randomIntegerInRange(0, 5); // 2Returns a random number in the specified range.
Use Math.random() to generate a random value, map it to the desired range using multiplication.
const randomNumberInRange = (min, max) => Math.random() * (max - min) + min;Examples
randomNumberInRange(2, 10); // 6.0211363285087005Rounds a number to a specified amount of digits.
Use Math.round() and template literals to round the number to the specified number of digits.
Omit the second argument, decimals to round to an integer.
const round = (n, decimals = 0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);Examples
round(1.005, 2); // 1.01Returns the standard deviation of an array of numbers.
Use Array.reduce() to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then
determine the standard deviation.
You can omit the second argument to get the sample standard deviation or set it to true to get the population standard deviation.
const standardDeviation = (arr, usePopulation = false) => {
const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
return Math.sqrt(
arr
.reduce((acc, val) => acc.concat(Math.pow(val - mean, 2)), [])
.reduce((acc, val) => acc + val, 0) /
(arr.length - (usePopulation ? 0 : 1))
);
};Examples
standardDeviation([10, 2, 38, 23, 38, 23, 21]); // 13.284434142114991 (sample)
standardDeviation([10, 2, 38, 23, 38, 23, 21], true); // 12.29899614287479 (population)Performs speech synthesis (experimental).
Use SpeechSynthesisUtterance.voice and window.speechSynthesis.getVoices() to convert a message to speech.
Use window.speechSynthesis.speak() to play the message.
Learn more about the SpeechSynthesisUtterance interface of the Web Speech API.
const speechSynthesis = message => {
const msg = new SpeechSynthesisUtterance(message);
msg.voice = window.speechSynthesis.getVoices()[0];
window.speechSynthesis.speak(msg);
};Examples
speechSynthesis('Hello, World'); // // plays the messageWrites a JSON object to a file.
Use fs.writeFile(), template literals and JSON.stringify() to write a json object to a .json file.
const fs = require('fs');
const JSONToFile = (obj, filename) =>
fs.writeFile(`${filename}.json`, JSON.stringify(obj, null, 2));Examples
JSONToFile({ test: 'is passed' }, 'testJsonFile'); // writes the object to 'testJsonFile.json'Returns an array of lines from the specified file.
Use readFileSync function in fs node package to create a Buffer from a file.
convert buffer to string using toString(encoding) function.
creating an array from contents of file by spliting file content line by line (each \n).
const fs = require('fs');
const readFileLines = filename =>
fs
.readFileSync(filename)
.toString('UTF8')
.split('\n');Examples
/*
contents of test.txt :
line1
line2
line3
___________________________
*/
let arr = readFileLines('test.txt');
console.log(arr); // ['line1', 'line2', 'line3']Removes any properties except the ones specified from a JSON object.
Use Object.keys() method to loop over given JSON object and deleting keys that are not included in given array.
Also if you give it a special key (childIndicator) it will search deeply inside it to apply function to inner objects too.
const cleanObj = (obj, keysToKeep = [], childIndicator) => {
Object.keys(obj).forEach(key => {
if (key === childIndicator) {
cleanObj(obj[key], keysToKeep, childIndicator);
} else if (!keysToKeep.includes(key)) {
delete obj[key];
}
});
return obj;
};Examples
const testObj = { a: 1, b: 2, children: { a: 1, b: 2 } };
cleanObj(testObj, ['a'], 'children'); // { a: 1, children : { a: 1}}Creates an object from the given key-value pairs.
Use Array.reduce() to create and combine key-value pairs.
const objectFromPairs = arr => arr.reduce((a, v) => ((a[v[0]] = v[1]), a), {});Examples
objectFromPairs([['a', 1], ['b', 2]]); // {a: 1, b: 2}Creates an array of key-value pair arrays from an object.
Use Object.keys() and Array.map() to iterate over the object's keys and produce an array with key-value pairs.
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);Examples
objectToPairs({ a: 1, b: 2 }); // [['a',1],['b',2]])Returns a sorted array of objects ordered by properties and orders.
Uses a custom implementation of sort, that reduces the props array argument with a default value of 0, it uses destructuring to swap the properties position depending on the order passed. If no orders array is passed it sort by 'asc' by default.
const orderBy = (arr, props, orders) =>
[...arr].sort((a, b) =>
props.reduce((acc, prop, i) => {
if (acc === 0) {
const [p1, p2] = orders && orders[i] === 'desc' ? [b[prop], a[prop]] : [a[prop], b[prop]];
acc = p1 > p2 ? 1 : p1 < p2 ? -1 : 0;
}
return acc;
}, 0)
);Examples
const users = [
{ name: 'fred', age: 48 },
{ name: 'barney', age: 36 },
{ name: 'fred', age: 40 },
{ name: 'barney', age: 34 }
];
orderBy(users, ['name', 'age'], ['asc', 'desc']); // [{name: 'barney', age: 36}, {name: 'barney', age: 34}, {name: 'fred', age: 48}, {name: 'fred', age: 40}]
orderBy(users, ['name', 'age']); // [{name: 'barney', age: 34}, {name: 'barney', age: 36}, {name: 'fred', age: 40}, {name: 'fred', age: 48}]Retrieve a property that indicated by the selector from an object.
If the property does not exists returns undefined.
const select = (from, selector) =>
selector.split('.').reduce((prev, cur) => prev && prev[cur], from);Examples
const obj = { selector: { to: { val: 'val to select' } } };
select(obj, 'selector.to.val'); // 'val to select'Creates a shallow clone of an object.
Use Object.assign() and an empty object ({}) to create a shallow clone of the original.
const shallowClone = obj => Object.assign({}, obj);Examples
const a = { x: true, y: 1 };
const b = shallowClone(a);
a === b; // falseChecks if the predicate (second argument) is truthy on all elements of a collection (first argument).
Use Array.every() to check if each passed object has the specified property and if it returns a truthy value.
const truthCheckCollection = (collection, pre) => collection.every(obj => obj[pre]);Examples
truthCheckCollection([{ user: 'Tinky-Winky', sex: 'male' }, { user: 'Dipsy', sex: 'male' }], 'sex'); // trueGenerates all anagrams of a string (contains duplicates).
Use recursion.
For each letter in the given string, create all the partial anagrams for the rest of its letters.
Use Array.map() to combine the letter with each partial anagram, then Array.reduce() to combine all anagrams in one array.
Base cases are for string length equal to 2 or 1.
const anagrams = str => {
if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
return str
.split('')
.reduce(
(acc, letter, i) =>
acc.concat(anagrams(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)),
[]
);
};Examples
anagrams('abc'); // ['abc','acb','bac','bca','cab','cba']Capitalizes the first letter of a string.
Use destructuring and toUpperCase() to capitalize first letter, ...rest to get array of characters after first letter and then Array.join('') to make it a string again.
Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lowercase.
const capitalize = ([first, ...rest], lowerRest = false) =>
first.toUpperCase() + (lowerRest ? rest.join('').toLowerCase() : rest.join(''));Examples
capitalize('fooBar'); // 'FooBar'
capitalize('fooBar', true); // 'Foobar'Capitalizes the first letter of every word in a string.
Use replace() to match the first character of each word and toUpperCase() to capitalize it.
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());Examples
capitalizeEveryWord('hello world!'); // 'Hello World!'Retuns number of vowels in provided string.
Use a regular expression to count the number of vowels (A, E, I, O, U) in a string.
const countVowels = str => (str.match(/[aeiou]/gi) || []).length;Examples
countVowels('foobar'); // 3
countVowels('gym'); // 0Escapes a string to use in a regular expression.
Use replace() to escape special characters.
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');Examples
escapeRegExp('(test)'); // \\(test\\)Converts a string from camelcase.
Use replace() to remove underscores, hyphens, and spaces and convert words to camelcase.
Omit the second argument to use a default separator of _.
const fromCamelCase = (str, separator = '_') =>
str
.replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
.replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2')
.toLowerCase();Examples
fromCamelCase('someDatabaseFieldName', ' '); // 'some database field name'
fromCamelCase('someLabelThatNeedsToBeCamelized', '-'); // 'some-label-that-needs-to-be-camelized'
fromCamelCase('someJavascriptProperty', '_'); // 'some_javascript_property'Repeats a string n times using String.repeat()
If no string is provided the default is "" and the default number of times is 2.
const repeatString = (str = '', num = 2) => {
return num >= 0 ? str.repeat(num) : str;
};Examples
repeatString('abc', 3); // 'abcabcabc'
repeatString('abc'); // 'abcabc'Reverses a string.
Use split('') and Array.reverse() to reverse the order of the characters in the string.
Combine characters to get a string using join('').
const reverseString = str =>
str
.split('')
.reverse()
.join('');Examples
reverseString('foobar'); // 'raboof'Alphabetically sorts the characters in a string.
Split the string using split(''), Array.sort() utilizing localeCompare(), recombine using join('').
const sortCharactersInString = str =>
str
.split('')
.sort((a, b) => a.localeCompare(b))
.join('');Examples
sortCharactersInString('cabbage'); // 'aabbceg'Converts a string to camelcase.
Break the string into words and combine them capitalizing the first letter of each word. For more detailed explanation of this Regex, visit this Site.
const toCamelCase = str => {
let s =
str &&
str
.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.slice(0, 1).toUpperCase() + x.slice(1).toLowerCase())
.join('');
return s.slice(0, 1).toLowerCase() + s.slice(1);
};Examples
toCamelCase('some_database_field_name'); // 'someDatabaseFieldName'
toCamelCase('Some label that needs to be camelized'); // 'someLabelThatNeedsToBeCamelized'
toCamelCase('some-javascript-property'); // 'someJavascriptProperty'
toCamelCase('some-mixed_string with spaces_underscores-and-hyphens'); // 'someMixedStringWithSpacesUnderscoresAndHyphens'Converts a string to kebab case.
Break the string into words and combine them using - as a separator.
For more detailed explanation of this Regex, visit this Site.
const toKebabCase = str =>
str &&
str
.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.toLowerCase())
.join('-');Examples
toKebabCase('camelCase'); // 'camel-case'
toKebabCase('some text'); // 'some-text'
toKebabCase('some-mixed_string With spaces_underscores-and-hyphens'); // 'some-mixed-string-with-spaces-underscores-and-hyphens'
toKebabCase('AllThe-small Things'); // "all-the-small-things"
toKebabCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML'); // "i-am-listening-to-fm-while-loading-different-url-on-my-browser-and-also-editing-xml-and-html"Converts a string to snake case.
Break the string into words and combine them using _ as a separator.
For more detailed explanation of this Regex, visit this Site.
const toSnakeCase = str => {
str &&
str
.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.toLowerCase())
.join('_');
};Examples
toSnakeCase('camelCase'); // 'camel_case'
toSnakeCase('some text'); // 'some_text'
toSnakeCase('some-javascript-property'); // 'some_javascript_property'
toSnakeCase('some-mixed_string With spaces_underscores-and-hyphens'); // 'some_mixed_string_with_spaces_underscores_and_hyphens'
toSnakeCase('AllThe-small Things'); // "all_the_smal_things"
toSnakeCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML'); // "i_am_listening_to_fm_while_loading_different_url_on_my_browser_and_also_editing_some_xml_and_html"Truncates a string up to a specified length.
Determine if the string's length is greater than num.
Return the string truncated to the desired length, with ... appended to the end or the original string.
const truncateString = (str, num) =>
str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;Examples
truncateString('boomerang', 7); // 'boom...'Converts a given string into an array of words.
Use String.split() with a supplied pattern (defaults to non-alpha as a regex) to convert to an array of strings. Use Array.filter() to remove any empty strings.
Omit the second argument to use the default regex.
const words = (str, pattern = /[^a-zA-Z-]+/) => str.split(pattern).filter(Boolean);Examples
words('I love javaScript!!'); // ["I", "love", "javaScript"]
words('python, javaScript & coffee'); // ["python", "javaScript", "coffee"]Returns the first non-null/undefined argument.
Use Array.find() to return the first non null/undefined argument.
const coalesce = (...args) => args.find(_ => ![undefined, null].includes(_));Examples
coalesce(null, undefined, '', NaN, 'Waldo'); // ""Returns a customized coalesce function that returns the first argument that returns true from the provided argument validation function.
Use Array.find() to return the first argument that returns true from the provided argument validation function.
const coalesceFactory = valid => (...args) => args.find(valid);Examples
const customCoalesce = coalesceFactory(_ => ![null, undefined, '', NaN].includes(_));
customCoalesce(undefined, null, NaN, '', 'Waldo'); // "Waldo"Extends a 3-digit color code to a 6-digit color code.
Use Array.map(), split() and Array.join() to join the mapped array for converting a 3-digit RGB notated hexadecimal color-code to the 6-digit form.
String.slice() is used to remove # from string start since it's added once.
const extendHex = shortHex =>
'#' +
shortHex
.slice(shortHex.startsWith('#') ? 1 : 0)
.split('')
.map(x => x + x)
.join('');Examples
extendHex('#03f'); // '#0033ff'
extendHex('05a'); // '#0055aa'Returns the native type of a value.
Returns lowercased constructor name of value, "undefined" or "null" if value is undefined or null
const getType = v =>
v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();Examples
getType(new Set([1, 2, 3])); // "set"Converts a color code to a rgb() or rgba() string if alpha value is provided.
Use bitwise right-shift operator and mask bits with & (and) operator to convert a hexadecimal color code (with or without prefixed with #) to a string with the RGB values. If it's 3-digit color code, first convert to 6-digit version. If an alpha value is provided alongside 6-digit hex, give rgba() string in return.
const hexToRGB = hex => {
let alpha = false,
h = hex.slice(hex.startsWith('#') ? 1 : 0);
if (h.length === 3) h = [...h].map(x => x + x).join('');
else if (h.length === 8) alpha = true;
h = parseInt(h, 16);
return (
'rgb' +
(alpha ? 'a' : '') +
'(' +
(h >>> (alpha ? 24 : 16)) +
', ' +
((h & (alpha ? 0x00ff0000 : 0x00ff00)) >>> (alpha ? 16 : 8)) +
', ' +
((h & (alpha ? 0x0000ff00 : 0x0000ff)) >>> (alpha ? 8 : 0)) +
(alpha ? `, ${h & 0x000000ff}` : '') +
')'
);
};Examples
hexToRGB('#27ae60ff'); // 'rgba(39, 174, 96, 255)'
hexToRGB('27ae60'); // 'rgb(39, 174, 96)'
hexToRGB('#fff'); // 'rgb(255, 255, 255)'Checks if the given argument is an array.
Use Array.isArray() to check if a value is classified as an array.
const isArray = val => !!val && Array.isArray(val);Examples
isArray(null); // false
isArray([1]); // trueChecks if the given argument is a native boolean element.
Use typeof to check if a value is classified as a boolean primitive.
const isBoolean = val => typeof val === 'boolean';Examples
isBoolean(null); // false
isBoolean(false); // trueChecks if the given argument is a function.
Use typeof to check if a value is classified as a function primitive.
const isFunction = val => val && typeof val === 'function';Examples
isFunction('x'); // false
isFunction(x => x); // trueChecks if the given argument is a number.
Use typeof to check if a value is classified as a number primitive.
const isNumber = val => typeof val === 'number';Examples
isNumber('1'); // false
isNumber(1); // trueChecks if the given argument is a string.
Use typeof to check if a value is classified as a string primitive.
const isString = val => typeof val === 'string';Examples
isString(10); // false
isString('10'); // trueChecks if the given argument is a symbol.
Use typeof to check if a value is classified as a symbol primitive.
const isSymbol = val => typeof val === 'symbol';Examples
isSymbol('x'); // false
isSymbol(Symbol('x')); // trueGenerates a random hexadecimal color code.
Use Math.random to generate a random 24-bit(6x4bits) hexadecimal number. Use bit shifting and then convert it to an hexadecimal String using toString(16).
const randomHexColorCode = () => {
let n = ((Math.random() * 0xfffff) | 0).toString(16);
return '#' + (n.length !== 6 ? ((Math.random() * 0xf) | 0).toString(16) + n : n);
};Examples
randomHexColorCode(); // "#e34155"
randomHexColorCode(); // "#fd73a6"
randomHexColorCode(); // "#4144c6"Converts the values of RGB components to a color code.
Convert given RGB parameters to hexadecimal string using bitwise left-shift operator (<<) and toString(16), then padStart(6,'0') to get a 6-digit hexadecimal value.
const RGBToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');Examples
RGBToHex(255, 165, 1); // 'ffa501'This algorithm is a simple hash-algorithm that hashes it input string s into a whole number.
Use split('') and Array.reduce() to create a hash of the input string, utilizing bit shifting.
const sdbm = str => {
let arr = str.split('');
return arr.reduce(
(hashCode, currentVal) =>
(hashCode = currentVal.charCodeAt(0) + (hashCode << 6) + (hashCode << 16) - hashCode),
0
);
};Examples
console.log(sdbm('name')); // -3521204949
console.log(sdbm('age')); // 808122783Measures the time taken by a function to execute.
Use console.time() and console.timeEnd() to measure the difference between the start and end times to determine how long the callback took to execute.
const timeTaken = callback => {
console.time('timeTaken');
const r = callback();
console.timeEnd('timeTaken');
return r;
};Examples
timeTaken(() => Math.pow(2, 10)); // 1024
// (logged): timeTaken: 0.02099609375msUse toLocaleString() to convert a float-point arithmetic to the Decimal mark form. It makes a comma separated string from a number.
const toDecimalMark = num => num.toLocaleString('en-US');Examples
toDecimalMark(12305030388.9087); // "12,305,030,388.9087"Adds an ordinal suffix to a number.
Use the modulo operator (%) to find values of single and tens digits.
Find which ordinal pattern digits match.
If digit is found in teens pattern, use teens ordinal.
const toOrdinalSuffix = num => {
const int = parseInt(num),
digits = [int % 10, int % 100],
ordinals = ['st', 'nd', 'rd', 'th'],
oPattern = [1, 2, 3, 4],
tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
return oPattern.includes(digits[0]) && !tPattern.includes(digits[1])
? int + ordinals[digits[0] - 1]
: int + ordinals[3];
};Examples
toOrdinalSuffix('123'); // "123rd"Generates a UUID.
Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const UUIDGenerator = () =>
([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
(c ^ (crypto.getRandomValues(new Uint8Array(1))[0] & (15 >> (c / 4)))).toString(16)
);Examples
UUIDGenerator(); // '7982fcfe-5721-4632-bede-6000885be57d'Returns true if the given value is a number, false otherwise.
Use !isNaN in combination with parseFloat() to check if the argument is a number.
Use isFinite() to check if the number is finite.
Use Number() to check if the coercion holds.
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;Examples
validateNumber('10'); // trueIcons made by Smashicons from www.flaticon.com is licensed by CC 3.0 BY.