cheat-sheet.md

JavaScript Cheatsheet

JavaScript (or JS)

A popular programming language commonly used to create interactive effects within web browsers.

variable

A place to store values, can store any kind of information (data types): numbers, words, collections of data

undefined variable

A variable that has no value

to declare variable

To create a variable - done by using:

let variableName = value;

to initialize variable

Set (give) some value to a variable.

value types

string

A set of characters, word(s), phrase. To initialize variable with a string you need to put this string into quotes.

boolean

Boolean variable represent a logical value True or False

array

An ordered list of values, can store different types of data inside

operator

Mathematical operators, such as: +, -, *, /, >, <, = etc

comments

Comments are notes that you can leave for yourself or another person, a note that a computer will not read. You can write a comment on a new line or on the same line after code as so:

let variableName; // I’m your comment

Single line comments start with // and continue for the entire line Multi line comments are placed between /* .. */ and can end at any point on a line

function

A separable, reusable piece of code. It takes some input, does some manipulation on it and returns an output.

to declare function

To create a function

argument

A value input that functions can accept

if/else statement

if is used to decide if lines of code should be executed, else - gives an alternative set of instructions.

Example:

if (x > 5) {
  console.log("X bigger than 5");
}
else {
  console.log("X smaller than or equal to 5");
}

Iterating/Loops

while loop

It repeats code over and over again until some condition is met.

for loop

This loop is similar to ‘while loop’, just with a set amount of repetition. You declare counter in the statement as so:

for (let i = 0; i < 5; i++) {
  do something 5 times
}

infinite loop

This is an error which means that a loop does not stop.

In order to avoid this error each loop should have some condition so it can stop, and contain some way to trigger the condition.

object

A collection of properties

event

A type of object that is created when a user interacts with a web page. For example, JavaScript creates an event when a user clicks on a button.

CSS

Stands for Cascading Style Sheets. CSS describes how HTML elements are to be displayed on screen. It is presentation.

HTML

Stands for Hyper Text Markup Language. It is a structure of the elements on the page.

DOM

Stands for Document Object Model. It defines the logical structure of documents and the way a document is accessed and manipulated.

scope

Scope is the set of variables, objects, and functions that you can access.

console

A method of interacting with the system. In order to write to the browser console, you could use console.log(‘Hello World’). This would write Hello World in the browser console.