JavaScript Almanac

Best JavaScript Idioms and some shortcusts

Sites

• From Mediasuite

Instead of this

if("foobar".indexOf("foo") > -1) 

Do this

if(~"foobar".indexOf("foo"))

Instead of this

var foo = Math.floor(2.333)

Do this

var foo = ~~2.333

Instead of this

var foo = parseFloat("12.4")
var bar = parseInt("12", 10)

Do this

var foo = +"12.4"
var bar = +"12"

Instead of this

if(isNaN(foo))

Do this

if(foo != foo)

Instead of this

(function(){ ... })()

Do this

!function(){ ... }()

Convert anything to a boolean by prefixing it with !!

var isFoo = !!foo

null vs undefined

• best SO explanation
• null: has type object but no value
• undefined: has no type and no value

Hoisting

• var hoisting
• Hoisting is JavaScript's default behavior of moving declarations to the top
• Nice article from wsvincent
• JavaScript Hoisting
• DigitalOcean's explanation
• Hoisting precedence:
  • 1. Variable assignment takes precedence over function declaration
  • 2. Function declarations take precedence over variable declarations
  • variable assignment > function declaration > variable declaration
• To avoid Hoisting:
  • 1. using "use strict" directive on top
  • 2. using let and const inplace of var
  • 3. declaring all variables on top

Function Expression vs Function Declaration

• Declaration: defining a function for later use
  • hoisted to the top

function foo(){
    console.log("foo here");
}

// called with the name of the function
foo();

• Expression: storing a function in a variable
  • not hoisted to the top

var x = function (a, b) {return a * b};

// called using the vairable name
x(4,5);//20

BEST: The Ultimate Guide to Execution Contexts, Hoisting, Scopes, and Closures in JavaScript

• more on closures

[[Prototype]] vs __proto__ vs prototype

• best stackoverflow summary
• nice article from levelup
• understanding prototype
• awesome site: JS docs
  • part 1: What exactly is a prototype?
  • part 2: What does a prototype do?

The new keyword in javascript

• What is the new keyword in JavaScript?
• mdn - doc
• Against new keyword

They all does the same thing: Tomato Potato

const abc = {
  salute: "",
  greet: function() {
    this.salute = "Hello";
    console.log(this.salute); //Hello
    const setFrench = function(newSalute) {
      this.salute = newSalute;
    };
    setFrench("Bonjour");
    console.log(this.salute); //Bonjour
  }
};

setTimeout(abc.greet.bind(abc));        // setTimeout + bind
setTimeout(()=> abc.greet.call(abc));   // setTimeout + call 
setTimeout(()=> abc.greet.apply(abc));  // setTimeout + apply

setInterval(abc.greet.bind(abc));        // setInterval + bind 
setInterval(()=> abc.greet.call(abc));   // setInterval + call 
setInterval(()=> abc.greet.apply(abc));  // setInterval + apply

(abc.greet)();                          // function wrap (only)
(abc.greet.bind(abc))();                // bind  + function wrap
(() => abc.greet.call(abc))();          // call  + function wrap
(() => abc.greet.apply(abc))();         // apply + function wrap

JQuery and Ajax

• Document Ready Function: A page can't be manipulated safely until the document is "ready." jQuery detects this state of readiness for you. Code included inside $( document ).ready() will only run once the page Document Object Model (DOM) is ready for JavaScript code to execute.

$(document).ready(function(){})

Shorthand equivalent(alias):

$(function(){})

JavaScript equivalent of the JQuery code above

• event.preventDefault() vs return false

Object literal vs JSON

• best stackoverflow explanation
• JSON has to be:
  • Key values must be quoted
  • Strings must be quoted with " and not '
  • You have a more limited range of values (e.g. no functions allowed)

JS versions and release dates: source: greycampus

 - ES1 1997
 - ES2 1998
 - ES3 1999
 - ES4 Abandoned
 - ES5 2009
 - ES6 2015
 - ES7 2016
 - ES8 2017
 - ES9 2018