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Class

/** Class representing a point. */
class Point {
    /**
     * Create a point.
     *
     * @param {number} x - The x value.
     * @param {number} y - The y value.
     *
     * @return {number} The x value.
     *
     */
    constructor(x, y) {
        // ...
    }

JavaScript (ES5 or lower)

Truthy & Falsy

Truthy

In JavaScript, a truthy value is a value that translates to true when evaluated in a Boolean context. All values are truthy unless they are defined as falsy.

Examples

if (true)
if ({})
if ([])
if (42)
if ('foo')
if (new Date())
... and everything else (unless defined as falsy)

Falsy

A falsy value is a value that translates to false when evaluated in a Boolean context.

Seven cases

if (false)
if (null)
if (undefined)
if (0)
if (NaN)
if ('')
if ("")

Function composition

Functions can be combined to form new functions through function composition. The function addThenSquare is made by combining the functions add and square.

const add = function(x, y) {
    return x + y;
};

const square = function(x) {
    return x * x;
};

const addThenSquare = function(x, y) {
    return square(add(x, y));
};

Prototype

Every JavaScript object has a prototype which is also an object. All JavaScript objects inherit their properties and methods from their prototype.

function Something() {} // note capital letter and fact that function is an object in JS

Something.prototype.bar = true; // this could also be a method/function
let something = new Something();

something.bar; // true
something instanceof Something; // true

ECMAScript 6

A transpiler takes ES6 source code and generates ES5 code that can run in every browser - e.g. Traceur or Babeljs.

Modules (import and export)

Export

Export statement is used to export functions, objects or primitives from a given file.

export { name1, name2 };
export { variable1 as name1, variable2 as name2 };
export let name1, name2;
export let name1 = ..., name2 = ...

There are two different types of export:

a) Named exports:

export { myFunction }; // exports a function declared earlier export
const foo = Math.sqrt(2); // exports a constant

b) Default exports (only one per script):

export default function() {} export default function name() {}
export { name1 as default, name2 };

Re-exporting means adding another module’s exports to those of the current module.

export * from 'other-module-name';
export { name1, name2 } from 'other-module-name';

Import

The import statement is used to import functions, objects or primitives that have been exported from an external module, another script.

import nameForDefault from 'module-name';
import * as name from 'module-name';
import { name } from 'module-name';
import { name as anotherName } from 'module-name';
import { name1, name2 } from 'module-name';

Class

Class definition

class Shape {
    constructor (id, x, y) {
        this.id = id
        this.move(x, y)
    }
    move (x, y) {
        this.x = x
        this.y = y
    }
}

Class inheritance, base class access

class Shape {
    ...
    toString() {
        return `Shape(${this.id})`;
    }
}

class Rectangle extends Shape {
    constructor (id, x, y, width, height) {
        super(id, x, y)
        ...
    }
    toString() {
        return "Rectangle > " + super.toString();
    }
}

Using extends with built-in objects

class myDate extends Date {
    constructor() {
        super();
    }

    getFormattedDate() {
        const months = ['Jan', 'Feb', 'Mar', etc.];
        return this.getDate() + "-" + months[this.getMonth()] + "-" + this.getFullYear();
    }
}

Static members

class Circle extends Shape {
    ...
    static defaultCircle() {
        return new Circle('default', 0, 0, 100)
    }
}

const defCircle = Circle.defaultCircle();

Template literals

By using back-tick you can use variables with strings.

`${variable} and lorem ipsum.`

Or even write multi line text.

`Lorem ipsum
and another line.`

let

In pretty much any other languages, a variable is declared where the declaration is done. But in JS, there is a concept, called hoisting, which actually declares a variable at the top of the function, even if you declared it later. See more

By using let the variable name is now restricted to its block.

function getPonyFullName(pony) {
  if (pony.isChampion) {
    let name = 'Champion ' + pony.name;
    return name;
  }
  // name is not accessible here
  return pony.name;
}

Constants

When you declare a variable with const, it has to be initialized and you can’t assign another value later.

const PONIES_IN_RACE = 6;

Creating objects

Example:

function createPony() {
    let name = 'Rainbow Dash';
    let color = 'blue';
    return { name: name, color: color };
}

can be simplified to

function createPony() {
    let name = 'Rainbow Dash';
    let color = 'blue';
    return { name, color };
}

Destructuring assignment

There is a shortcut for assigning variables from objects or arrays.

const { something, somethingElse } = object;

Will produce the same as:

const something = object.something;
const somethingElse = object.somethingElse;

Spread operator

The spread syntax allows an expression to be expanded.

function myFunction(x, y, z) {}

let args = [0, 1, 2];
myFunction(...args);

Or

let parts = ['shoulders', 'knees'];
let lyrics = ['head', ...parts, 'and', 'toes']; // ["head", "shoulders", "knees", "and", "toes"]

You can also use it for shallow copy of object

const shallowSomeObject = {...someObject};
shallowSomeObject.newProperty = 'some string';

Default parameters and values

const link = function(color = 'red', url = 'http://some-url.com') {
    ...
}

Promises

The Promise object is used for deferred (postponed) and asynchronous computations. A Promise represents an operation that hasn't completed yet, but is expected in the future.

A Promise is in one of these states:

  • pending: initial state, not fulfilled or rejected.
  • fulfilled: meaning that the operation completed successfully.
  • rejected: meaning that the operation failed.

a) Example

let promise = new Promise(function(resolve, reject) {

    // do something
    if (true) {
        resolve('It worked!');
    }
    else {
        reject('An error.'));
    }
});

Here's how you use that promise:

promise
    .then(function(result) {
        console.log(result); // It worked!
    })
    .catch(function(err) {
        console.log(err); // An error.
    });

b) Another example:

function msgAfterTimeout(msg, time) {
    return new Promise((resolve, reject) => {
        setTimeout(() => resolve(msg), time)
    })
}

msgAfterTimeout("Breakfast is served.", 500).then(result => console.log(result));

Arrow functions

The new arrow function syntax is the fat arrow operator (⇒). It is useful for callbacks and anonymous functions.

In ES5:

getUser(login)
    .then(function(user) {
        return getRights(user);
    })
    .then(function(rights) {
        return updateMenu(rights);
    })

Using fat arrow operator in ES6:

getUser(login)
    .then(user => getRights(user))
    .then(rights => updateMenu(rights))

No need to write user ⇒ return getRights(user). But if we did have a block, we would need the explicit return:

getUser(login)
    .then(user => {
        console.log(user);
        return getRights(user);
    })
    .then(rights => updateMenu(rights))

React

JSX

This is a sample of JSX (JavaScript XML).

let HelloWorld = React.createClass({
    render: () => {
        return
            <div>
                <h1>Hello World</h1>
                <p>This is some text</p>
            </div>
    }
});

React.render(<Hello World />, document.body);

Properties

This is sample of using props.

let HelloWorld = React.createClass({
    render: () => {
        return
            <div>
                <h1>{this.props.text}</h1>
                <p>{this.props.children}</p>
            </div>
    }
});

React.render(
    <div>
        <Hello World text="Hello World" />
        <Hello World>
            This is some text
        </Hello World>
    </div>
    , document.getElementById('some-container')
);

Types of properties

Example of determining types.

    propTypes = {
        propFunction: React.PropTypes.func,
        propObject: React.PropTypes.object,
        propWithinObject: React.PropTypes.shape({
            sampleProp: React.PropTypes.oneOfType([
                React.PropTypes.number,
                React.PropTypes.string
            ]).isRequired,
            anotherSampleProp: React.PropTypes.isRequired
        }).isRequired
    };

Bind this

It’s not always clear what this is going to refer to in your code. As functions in JS are objects, every function has it own this. Samples:

Alias This

    var component = this;
    component.setState({ loading: true });

    fetch('/').then(function loaded() {
        component.setState({ loading: false });
    });

Bind This

    this.setState({ loading: true });

    fetch('/').then(function loaded() {
        this.setState({ loading: false });
    }.bind(this));

React Component Methods

React allows you to define arbitrary methods on your component classes and these methods are automatically bound with the correct context for this when you create your components with React.createClass. This allows you move your callback code out onto your component.

React.createClass({
    componentWillMount: function() {
        this.setState({ loading: true });

        fetch('/').then(this.loaded);
    },
    loaded: function loaded() {
        this.setState({ loading: false });
    }
});

ES2015 Arrows

They always use the value of this from the enclosing scope.

    this.setState({ loading: true });

    fetch('/').then(() => {
        this.setState({ loading: false });
    });

Stateless functional components

A simpler way to define components called stateless functional components. These components use plain JavaScript functions. Stateless functional components don’t support state or lifecycle methods.

Samples:

const ListItem = (props) => <li>{props.item.name}</li>;

or

const List = ({ items }) => (
    <ul>
        {items.map((item) => <ListItem item={item} />)}
    </ul>
);

or

const Body = (props) => {
    let items = transformItems(props.rawItems);

    return (
        <div>
            <h1>{props.header}</h1>
            <List items={items} />
        </div>
    );
};

Body.propTypes = {
    rawItems: React.PropTypes.array.isRequired,
};

Lifecycle methods

These methods are executed at specific points in a component's lifecycle.

componentWillMount

Invoked only once, both on the client and server, immediately before the initial rendering occurs.

See sample

If you call setState within this method, render() will see the updated state and will be invoked only once (ignoring that state changed).

See sample

Params: none

Animations

componentWillMount() {
    this.animationValue = new Animated.Value();

    this.animationValue.addListener(value => {
        this.animationStep(value);
    });
}

componentDidMount() {
    this.animateIt();
}

animateIt() {
    this.animationValue.setValue(0);

    Animated.timing(this.animationValue, {
        toValue: 100,
        duration: this.props.animationDuration,
        easing: Easing.linear
    }).start();
}

animationStep(value) {
    // value will be between 1 - 100
    // use reference on element and change its data, e.g.
    ref.setAttribute('d', somethingCalculatedBasedOnValue);
}

See more at: - https://facebook.github.io/react-native/docs/animations.html - https://facebook.github.io/react-native/docs/animated.html

Git

Init

Initializes a repository in an existing directory. This will create .git hidden folder, a location where Git operates.

git init

Status

Shows the working tree status.

git status

Add

This command updates the index using the current content found in the working tree, to prepare the content staged for the next commit.

git add some-file.txt

Wildcards are supported, e.g. git add '*.txt' or you can add all files by git add .

Commit

Check how to properly write a git commit message.

Records changes to the repository. By using -m flag, a custom message will be added with commit.

git commit -m "Some message"

By using -a flag, command will also do git add .

git commit -a -m "Some message"

Log

Shows local commit logs.

git log

Shows remote commit logs.

git log origin/master

Shows local commit logs in one line / commit.

git log --oneline

Shows local commit logs with graphic appearance.

git log --graph

Shows files changed in local commit logs

git log --name-only

Remote add

Manages set of tracked repositories.

git remote add origin some-url

Push

Updates remote refs along with associated objects. The flag -u tells Git to remember the parameters, so that next time we can simply run git push and Git will know what to do.

git push -u origin master

Pull

Fetches from and integrate with another repository or a local branch.

git pull origin master

Diff

Show changes between commits, commit and working tree, etc.

git diff

Shows difference of most recent commit, which is referred using the HEAD pointer.

git diff HEAD

Shows staged difference.

git diff --staged

Clean

Removes untracked files from the working tree.

git clean -f

Flag f will force deletion, otherwise git will refuse it.

Reset

Unstages files.

git reset some-file.txt

Flag soft will move HEAD 1 commit back and put changes as they were not commited yet, so you can commit them again.

git reset --soft HEAD~1

Flag hard will move HEAD 1 commit back and delete changes.

git reset --hard HEAD~1

Revert

It will revert commit by adding a commit (so you can see the history of what has been reverted).

git revert commitId

Checkout

Changes file back to how it was at the last commit.

git checkout -- some-file.txt

Branches

Creates new branch

git branch new_branch_name

Deletes branch

git branch -d branch_name

Checkouts to new branch

git checkout new_branch_name

Merges branch into checkouted branch (e.g. first checkout to master branch, then merge develop branch into)

git merge name_of_branch

Shows merged branches that had been merged at any time

git branch --merged

Clone

It will clone remote repository to local one.

git clone some-url

Remote

Set remote repository

git remote add origin some-url

Show remote repository

git remote -v

Tags

Listing tags

git tag

Creating annotated tag

git tag -a v1.4 -m "my version 1.4"
git push origin --tags

Deleting tag

git tag -d v1.4

Submodules

Go to root folder.

git submodule add some-repo-url some-folder

Git Flow

Git-flow are a set of git extensions to provide high-level repository operations for Vincent Driessen's branching model.

Init

Start using git-flow by initializing it inside an existing git repository

git flow init

Feature

This action creates a new feature branch based on develop and switches to it:

git flow feature start new-branch-name

Finish the development of a feature. This action performs the following:

  • merges existing-branch-name branch into develop branch
  • removes the existing-branch-name branch
  • switches back to develop branch
git flow feature finish existing-branch-name

Publish a feature to the remote server so it can be used by other users:

git flow feature publish existing-branch-name

TypeScript

Why TypeScript

There are two main goals of TypeScript:

  • Provide an optional type system for JavaScript.
  • Provide planned features from future JavaScript editions to current JavaScript engines

sample.js (JavaScript)

let foo = 123;

sample.ts (TypeScript)

let foo: number = 123

Types increase your agility when doing refactoring. Its better for the compiler to catch errors than to have things fail at runtime.

Types are structural

interface Point2D {
    x: number;
    y: number;
}
interface Point3D {
    x: number;
    y: number;
    z: number;
}

var point2D: Point2D = { x: 0, y: 10, }
var point3D: Point3D = { x: 0, y: 10, z: 20 }
function iTakePoint2D(point: Point2D) { /* do something */ }

iTakePoint2D(point2D); // exact match okay
iTakePoint2D(point3D); // extra information okay
iTakePoint2D({ x: 0 }); // Error: missing information `y`

Reactive programming

Reactive programming is a way to build an app using events and reacting to them, using Reactive Extensions library like RxJS (RxJava...). Apps have evolved to be more real-time: e.g. "likes" to some content can be reflected in real time to other connected users.

Listener is called an observer, and the stream, an observable. A stream is an ordered sequence of events. This is well-known design pattern: the observer pattern.

Observables are very close to arrays. An array is a collection of values, like an observable. An observable only adds the concept of values over time: in an array, you have all the values at once, while the values will come over time in an observable, maybe every few minutes.

Every observable, just like every array, can be transformed:

  • take(n) will pick the n first events
  • map(fn) will apply fn to each event and return the result
  • filter(predicate) will only let through the events that fulfill the predicate
  • reduce(fn) will apply fn to every event to reduce the stream to a single value
  • merge(s1, s2) will merge the streams
  • subscribe(fn) will apply fn to each event it receives
  • and much more...
[1, 2, 3, 4, 5]
    .map(x => x * 2)
    .filter(x => x > 5)
    .forEach(x => console.log(x)); // 6, 8, 10

RxJS let us build an observable from an array.

Observable.fromArray([1, 2, 3, 4, 5])
    .map(x => x * 2)
    .filter(x => x > 5)
    .subscribe(x => console.log(x)); // 6, 8, 10

But an observable is more than a collection. It is an asynchronous collection, where the events arrive over time.

let input = $('input');

Observable.fromEvent(input, 'keyup')
    .subscribe(() => console.log('keyup!'));

    input.trigger('keyup'); // logs 'keyup!'
    input.trigger('keyup'); // logs 'keyup!'

You can build observables from AJAX requests, browser events, Web sockets responses, a promise, whatever you can think of.

Observable.create takes a function that will emit events on the observer given as parameter. Here it simply emits one event for the demonstration.

let observable = Observable.create((observer) => observer.next('hello'));

observable.subscribe((value) => console.log(value));
// logs 'hello'

Here, the range method we are using to create the events will iterate from 1 to 5 and then emit the 'completed' signal:

Observable.range(1, 5)
    .map(x => x * 2)
    .filter(x => x > 5)
    .subscribe(x => console.log(x), error => console.log(error), () => console.log('done'));
    // 6, 8, 10, done

Reactive programming in Angular 2

The EventEmitter has a method subscribe() to react to events and this method can receive three parameters:

  • a method to react on events
  • a method to react on errors
  • a method to react on completion
let emitter = new EventEmitter();

emitter.subscribe(
    value => console.log(value),
    error => console.log(error),
    () => console.log('done')
);

emitter.emit('hello');
emitter.emit('there');
emitter.complete();

// logs 'hello', then 'there', then 'done'

Subject

A Subject is a sort of bridge that is available in some implementations of ReactiveX that acts both as an Observer and as an Observable. Because it is an observer, it can subscribe to one or more Observables, and because it is an Observable, it can pass through the items it observes by reemitting them, and it can also emit new items.

spinner$: Subject<boolean> = new Subject();
spinner: boolean = false;

this.spinner$.next(this.spinner);

this.spinner$.subscribe((spinner) => {
  console.log(spinner); // should output false
});

Angular 1.5

Components

Component is normally build out of controller and template.

Component file

e.g. avatar.component.js

(function() {
    'use strict';

    angular
        .module('SomeModule')
        .component('avatar', {
            controller: 'AvatarController',
            controllerAs: 'avatarCtrl', // alias for controller name in view instead of $ctrl
            template: function($templateCache) {
                return $templateCache.get('./some-path/avatar.component.html');
            },
            transclude: true,
            bindings: {
                url: '@'
            }
        });

})();

Controller file

e.g. avatar.controller.js

(function() {
    'use strict';

    angular
        .module('SomeModule')
        .controller('AvatarController', AvatarController);

    function AvatarController() {
        var vm = this;
        vm.userAvatar = {};
        vm.hasAvatar = hasAvatar;

        function hasAvatar() {
            return !_.isUndefined(vm.url) && 
                   !_.isNull(vm.url) && 
                   vm.url.length > 0;
        }
    }

})();

View file

e.g. avatar.component.html

<div 
    class="user__avatar" 
    ng-if="avatarCtrl.userAvatar"
    ng-style="{'background-image': avatarCtrl.hasAvatar() ? 
               'url(' + avatarCtrl.url + ')' : 
               'url(/images/profile-avatar-placeholder.png)'}
">{{ avatarCtrl.someProperty }}</div>

// or two way data binding
<input type="text" ng-model="avatarCtrl.anotherProperty" />

// or event handling
<button ng-click="avatarCtrl.someFunction()"></button>

Lifecycle Hooks

$onInit()

This lifecycle hook will be executed when all controllers on an element have been constructed and after their bindings are initialized. This hook is meant to be used for any kind of initialization work of a controller.

    function SomeController() {
        var vm = this;
    
        vm.$onInit = function() {
            vm.foo = 'bar';
            vm.bar = 'foo';    
        };
    }
};

$onChanges(changes)

This hook allows us to react to changes of one-way bindings of a component.

In component

    bindings: {
        user: '<'
    }

In controller

    this.$onChanges = function(changes) {
        this.user = changes.user.currentValue;
    };

$onDestroy()

A hook that is called when its containing scope is destroyed. We can use this hook to release external resources, watches and event handlers.

$postLink()

// TODO

Bindings

    bindings: {
        user: '<' // For one-way bindings, using expression
        user: '=' // For two-way binding, using expression
        title: '@' // For attribute hardcoded value
        onDelete: '&' // Callbacks for component event 
    }

Three types of components

  1. Presentation (stateless) component

    • display user interface
    • stateless (dumb / pure)
    • data arrives via bindings (inputs), leaves via events (outputs)

  2. Business (stateful) component

    • access service & state
    • stateful (smart / impure / container)
    • do not provide interactive user interface
    • render other components

  3. View (router) component

    • build the current view (from URL)
    • specialist (smart / router) components
    • create components dynamically (via a Router)
    • can be entry points to the application

Communicating between components

Standard transcludion

It is transplanting DOM nodes into another component.

View file of controller

<modal heading="Here goes some heading">
    <p>Here goes some content.</p>
    <p>
        <a href="#">With some more content.</a>
    </p>
</modal>

View file of modal component

<div>
    <h2>{{modalCtrl.heading}}</h2>
    <a href="#" ng-click="modalCtrl.close()">X</a>
    <div ng-transclude></div> // NOTE: This will output content of modal component 
</div>

Component file

bindings: {
    heading: '@'
},
controllerAs: modalCtrl,
transclude: true,

Controller file

vm.close = function() { ... }

Multi-Slot transcludion

// TODO ## Angular 2

Components and directives

Components

  1. For register component we use @Component meta-data annotation.
  2. Component is a directive which use shadow DOM to create encapsulate visual behavior called components. Components are typically used to create UI widgets.
  3. Component is used to break up the application into smaller components.
  4. @View decorator or template url template are mandatory in the component.
import { Component, View } from 'angular2/angular2';

@Component({
    selector: 'message'
})

@View({
    template: `<h1>Hello Angular {{version}}</h1>`
})

class Message {
    constructor(public version: string) {}
}

<message></message>

Directives

  1. For register directives we use @Directive meta-data annotation.
  2. Directives is used to add behavior to an existing DOM element.
  3. Directive is use to design re-usable components.
  4. Directive don’t have View.
import { Directive } from 'angular2/angular2';

@Directive({
    selector: '[myDirective]',
    hostListeners: {
        'click': 'showMessage()'
    }
})

class Message {
    constructor() {}

    showMessage() {
        console.log('Hello Directive');
    }
}

<button myDirective>Click here</button>

In summary

Write a component when you want to create a reusable set of DOM elements of UI with custom behaviour. Write a directive when you want to write reusable behaviour to supplement existing DOM elements.

HostListener

Angular provides an easy way to listen to events on window or document. Regular way window.onScoll will not work - it's because the window object is instantiated outside Angular.

import { HostListener } from 'angular2/core';

class SomeClass {
    @HostListener('window:scroll', ['$event'])
        onScroll(event) {
            if ((window.innerHeight + window.scrollY) >= document.body.scrollHeight) {
            console.log('Bottom of page');
        }
    }
}

CSS

BEM

Blocks, Elements and Modifiers

A) Block

Standalone entity that is meaningful on its own.

Examples: header, container, menu, checkbox, input

B) Element

A part of a block that has no standalone meaning and is semantically tied to its block.

Examples: menu item, list item, checkbox caption, header title

C) Modifier

A flag on a block or element. Use them to change appearance or behavior.

Examples: disabled, highlighted, checked, fixed, size big, color yellow

Usage

The naming rules tell us to use block--modifier syntax.

HTML

<button class="button button--state-success">
    Success button
</button>
<button class="button button--state-danger">
    Danger button
</button>

CSS

.button { // rules for button }
.button--state-success { // rules for state-success modifier }
.button--state-danger  { // rules for state-danger modifier }

If there would be an element involved, we would use block__elem--modifier syntax.

How to correctly work with children selectors:

HTML

<div class="card">
    <div class="card__header">
        <h2 class="card__title">Title text here</h2>
    </div>
    <div class="card__body">
        <img class="card__img" src="some-img.png">

        <p class="card__text">Lorem ipsum dolor sit amet, consectetur</p>
        <p class="card__text">Adipiscing elit.
            <a href="/somelink.html" class="card__link">Pellentesque amet</a>
        </p>
    </div>
</div>

Don't use card__body__text__link as this will quickly get out of hand.

JSON Web Token

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object.

This information can be verified and trusted because it is digitally signed.

There are some scenarios where JSON Web Tokens are useful:

  • Authentication: This is the typical scenario for using JWT, once the user is logged in, each subsequent request will include the JWT, allowing the user to access routes, services, and resources that are permitted with that token.
  • Information Exchange: JSON Web Tokens are a good way of securely transmitting information between parties, because as they can be signed, for example using public/private key pairs, you can be sure that the senders are who they say they are.

JSON Web Tokens consist of three parts separated by dots ., which are:

  • Header
  • Payload
  • Signature

Therefore, a JWT typically looks like the following.

xxxxx.yyyyy.zzzzz

Header

For example:

{
    alg: 'HS256',
    typ: 'JWT'
}

Payload

The second part of the token is the payload, which contains the claims. There are three types of claims: reserved, public, and private claims.

An example of payload could be:

{
    sub: '1234567890',
    name: 'John Doe',
    admin: true
}

Signature

To create the signature part you have to take the encoded header, the encoded payload, a secret, the algorithm specified in the header, and sign that.

For example if you want to use the HMAC SHA256 algorithm, the signature will be created in the following way.

HMACSHA256(
  base64UrlEncode(header) + "." +
  base64UrlEncode(payload),
  secret)

The signature is used to verify that the sender of the JWT is who it says it is and to ensure that the message was't changed in the way.

Sample of encoded JWT:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh7HgQ

Design patterns

Publish / subscribe

This pattern uses an event system that sits between the objects wishing to receive notifications (subscribers) and the objects firing the events (publishers).

class PublishSubscribe {
    constructor() {
        this.topics = [];
    }

    subscribe(topic, callback) {

        // Create the topic if not yet created
        if (!this.topics[topic]) {
            this.topics[topic] = [];
        }

        // Add the callback to specific topic
        this.topics[topic].push(callback);
    }

    publish(topic, data) {

        // Returned false if the topic doesn't exist or there are no callbacks
        if (!this.topics[topic] || this.topics[topic].length === 0) {
            return false;
        }

        // Calling all callbacks for specific topic and passing data
        this.topics[topic].forEach((callback) => {
            callback(data || {});
        });
    }
}

const tryIt = new PublishSubscribe;

tryIt.subscribe('my-topic', alert);
tryIt.publish('my-topic', 'Hello World!');

The goal is to avoid dependencies between publisher and subscriber (so called decoupling).

Unix commands

Basics

cat

Show contents of the file.

cat some-file.txt

pwd

Show the name of the current working directory.

pwd

cd

Change the current working folder.

cd some-folder

cd ..    // move one folder up
cd /     // move to home folder
cd ~     // move to root

cp

Copy the file some-file-1.txt to the file some-file-2.txt in the current working folder.

cp some-file-1.txt some-file-2.txt

mv

Move or rename files.

mv some-file-1.txt some-file-2.txt    // Changes the names from "some-file-1.txt" to "some-file-2.txt"
mv /some-folder/some-file .           // Move the file from "some-file" from the folder "/some-folder" 
                                         to the current working folder.

rm

Remove the folder. Flag means remove recursively (deleting everything in folder)

rm -r folder

locate

Locates file or folder.

locate partial-name

ll

List all files in the current working directory in long listing format showing permissions, ownership, size, and time and date stamp.

ll

Using flag a will also show hidden files/folders.

ll -a

Mongo

Running services

sudo service mongodb start
sudo service mongodb stop
sudo service mongodb restart

or

brew services start mongodb
brew services stop mongodb

Client

Run client

mongo

Showing databases (with at least one record)

show dbs

Using specific database

use myDatabase

Showing collections

show collections

Create collection

db.createCollection("users", { autoIndexID : true })

Insert document

db.users.insert({"name" : "John"})

Showing documents

db.users.find().pretty()

Not to neglect

This title could also be What I've learned on my way from respective senior developers.

  • Writing clean and "cached" code is important. It doesn't really matter if a user sees his site in 30 ms (instead of 20 ms) but it matters if we can serve 800 sites/second (instead of just 500).

Resources

How to merge all md files

pandoc toc.md code-commenting.md javascript.md es6.md react.md git.md git-flow.md typescript.md reactive-programming.md angular-1-5.md angular-2.md css.md jwt.md design-patterns.md unix-commands.md mongo.md not-to-neglect.md resources.md note.md -f markdown -t markdown -s -o readme.md

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