JS: 2015 Features

What is ECMAScript 2015

• ECMAScript is the specification name for JavaScript.
• ECMAScript also known as ECMA-262, because it's number 262 of the spec organization called Ecma International.

• ECMAScript 2015 (aka ES6, ES2015, JS2015) is a major revision of the JavaScript language.
• ECMAScript 2015 is also known as ECMAScript 6 (ES6), because it is edition 6.

Over 10 major features are added to the language, effectively making JavaScript a new language.

Here is a quick overview of new features.

let

let is like var , but with a clean block-level scope.

• JS: let Declaration

const

const is for declaring constants. It's similar to let, except you can't change its value once set.

• JS: const Declaration

Arrow Function

you can write function like this

((x, y) => { return x + y; });

but no this Binding , and no arguments Object, no Function Name Hoisting .

• JS: Arrow Function

Function Argument Default Values

function parameter can specify a default value.

• JS: Function Argument Default Value

Rest Parameters

function can now specify to take any number of parameters, by syntax ...args

• JS: Function Rest Parameters

Destructuring Assignment

// destructuring assignment
let [x, y, z] = [3, 4, 6];

• JS: Destructuring Assignment

Object Literal Expression, Computed Property Keys

new syntax for object literal to have computed property key by an expression.

obj = {[expression]:value}

• JS: ES2015 Object Literal Expression Extensions

Object Literal Expression, Method Definition Shorthand

new syntax shorthand for defining methods in object literal expression.

obj = { method_name() {body}, etc };

• JS: ES2015 Object Literal Expression Extensions

__proto__

Allow the use of property key __proto__ to get/set parent.

• JS: Object.prototype.__proto__

Template String

allows you to embed variable or expression in a string, or have newline char.

• JS: Template String

Spread Operator

The spread operator is 3 dots followed by a array, like this: ...arrayX. What it does is effectively remove the bracket of the array.

• JS: Spread Operator

for-of Loop

for-of loop lets you properly loop thru an array, or new datatypes such as set and map, or any iterable object. Iterable object is a new concept, created just for for-of loops.

• JS: for-of Loop

Interface, Iterable, Iterator, Generator

• JS: Interface
• JS: Iterable Object
• JS: Iterator
• JS: Iterator Prototype
• JS: for-of Loop
• JS: Spread Operator
• JS: Generator
• JS: Generator Function

Set Object

Set object lets you have a data structure of set. That is, a collection of unique values.

// create a set, add value to it
var s = new Set();
s.add("6");
s.add("5");
s.add("6");
console.log(s); // Set { '5', '6' }

• JS: the Set Object Tutorial

Map Object

Map object lets you have a data structure of key value pairs. Map object is similar to Python's dictionary or Ruby's hash. Similar to JavaScript Object, but now designed to be used as a data structure.

const m = new Map();

// add new item
m.set(1, "n1");
m.set(2, "n2");

console.log(m); // Map { 1 => 'n1', 2 => 'n2' }

• JS: Map Object Tutorial

Reflect

The Reflect object is used as namespace to host a group of static functions. Reflect methods typically duplicate operator behavior in function form, or provides a more strict or improved version of existing methods.

• JS: Reflect

Class

class is a new keyword that lets you conveniently define object and its prototype.

New keywords are: class, constructor, static, extends, super.

• JS: Class

regex

New regex flag "u". For unicode. Treat string as sequence of unicode characters.

New regex flag "y". For “sticky”. This means next regex match call will start with lastIndex.

• JS: RegExp Flag

New value properties.

• RegExp.prototype.flags
• RegExp.prototype.sticky
• RegExp.prototype.unicode

New function properties.

• RegExp.prototype [ Symbol.match ](str)
• RegExp.prototype [ Symbol.replace ](str, replace)
• RegExp.prototype [ Symbol.search ](str)
• RegExp.prototype [ Symbol.split ](str, limit)

• JS: RegExp.prototype

New Array Properties

new array constructor properties

• Array.from
• Array.of

new array prototype properties

• Array.prototype.copyWithin
• Array.prototype.fill
• Array.prototype.find
• Array.prototype.findIndex
• Array.prototype.entries
• Array.prototype.keys
• Array.prototype.values
• Array.prototype[Symbol.iterator] (same as Array.prototype.values)
• Array.prototype [ Symbol.unscopables ]

• JS: Array.prototype

New String Properties

static methods

• String.fromCodePoint
• String.raw

string methods

• String.prototype.includes
• String.prototype.startsWith
• String.prototype.endsWith

• String.prototype.codePointAt
• String.prototype.repeat

• String.prototype.localeCompare
• String.prototype.normalize
• String.prototype[Symbol.iterator]

• JS: String.prototype

New Object Methods

• Object.assign
• Object.getOwnPropertySymbols
• Object.setPrototypeOf

New Function Properties

• Function.prototype[Symbol.hasInstance]

function property "name"

New Number Properties

• Number.isFinite
• Number.isInteger
• Number.isNaN
• Number.isSafeInteger
• Number.parseFloat
• Number.parseInt

• Number.EPSILON
• Number.MIN_SAFE_INTEGER
• Number.MAX_SAFE_INTEGER

• JS: Number Object

new Math methods

• Math [ Symbol.toStringTag ]
• Math.sign
• Math.fround
• Math.trunc
• Math.cbrt
• Math.expm1
• Math.log1p
• Math.log10
• Math.log2
• Math.hypot
• Math.sinh
• Math.cosh
• Math.tanh
• Math.asinh
• Math.acosh
• Math.atanh
• Math.clz32
• Math.imul

• JS: Math

html-like comments

• HTML-Like Comment

block-level function declaration

// es2015 block-level function declaration

function f() {
  function g(x) {
    return x + 1;
  }
  return g(1);
}

console.log(f()); // 2

Module, Keyword “import”, “export”

Import/Export

Unicode Escape Syntax

Now you can escape unicode by \u{4_to_6_hex_digits}

• JS: Unicode Escape Sequence

THE FOLLOWING IS WORK IN PROGRESS.

Syntax

• octal and binary literals
• new.target

Promise

Promise Tutorial

• String static methods
• String.prototype methods
• RegExp.prototype properties

Subclassing

• Array is subclassable
• RegExp is subclassable
• Function is subclassable
• Promise is subclassable
• miscellaneous subclassables

Misc

• prototype of bound functions
• Object static methods accept primitives
• own property order
• miscellaneous

Annex b

• Object.prototype.__proto__
• hoisted block-level function declaration
• String.prototype HTML methods
• RegExp.prototype.compile

ArrayBuffer

ECMAScript 2015 §Structured Data#sec-arraybuffer-objects

dataview object

ECMAScript 2015 §Structured Data#sec-dataview-objects

tail call optimisation (recursion)

ECMAScript 2015 §ECMAScript Language: Functions and Classes#sec-tail-position-calls

WeakSet

ECMAScript 2015 §Keyed Collection#sec-weakset-objects

WeakMap

ECMAScript 2015 §Keyed Collection#sec-weakmap-constructor