⛄️ ES6 Symbol polyfill in pure ES5
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symbol-es6.js

README.md

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Symbol-ES6

Provides support for ES6 Symbol API in ES5 for older JS environments i.e. older browsers or NodeJS.

ES6 Symbol polyfill in pure ES5.

Install

NPM

Install it from npm and require it before any other modules:

$ npm install --save symbol-es6
require("symbol-es6");

CDN

If you prefer CDN, then just insert it into your HTML page on the top of other scripts:

<script src="https://cdn.jsdelivr.net/npm/symbol-es6/dist/symbol-es6.min.js"></script>

Examples

"use strict";

var ES6 = require("symbol-es6");

console.log(Symbol("bar") === Symbol("bar")); //false

var sym = Symbol.for("bar");
var sym2 = Symbol("bar");

console.log(Symbol.for("bar") === sym); //true
console.log(sym === sym2); //false
console.log(Symbol.keyFor(sym)); //bar
console.log(Symbol.keyFor(sym2)); //undefined

console.log(Array.from("Hello")); //[ 'H', 'e', 'l', 'l', 'o' ]

var it = [1, 2].entries();

console.log(it.next()); //{ done: false, value: [ 0, 1 ] }
console.log(it.next()); //{ done: false, value: [ 1, 2 ] }
console.log(it.next()); //{ done: true, value: undefined }

it = [1, 2].keys();

console.log(it.next()); //{ done: false, value: 0 }
console.log(it.next()); //{ done: false, value: 1 }
console.log(it.next()); //{ done: true, value: undefined }

function Bar() {
}
console.log(Object.prototype.toString.call(new Bar())); //[object Object]

Bar.prototype[Symbol.toStringTag] = "Bar";

console.log(Object.prototype.toString.call(new Bar())); //[object Bar]

it = "Bar"[Symbol.iterator]();

console.log(it.next()); //{ done: false, value: 'B' }
console.log(it.next()); //{ done: false, value: 'a' }
console.log(it.next()); //{ done: false, value: 'r' }


console.log(ES6.isSymbol({})); //fasle
console.log(ES6.isSymbol(sym)); ///true

function Baz() {

}
console.log(ES6.instanceOf(89, Baz)); //false
Object.defineProperty(Baz, Symbol.hasInstance, {
   value: function (value) {
       return typeof value === "number";
   }
});
console.log(ES6.instanceOf(89, Baz)); //true

ES6.forOf([1, 2], function (v) {
    console.log(v);
});
//1
//2

console.log(ES6.spreadOperator([]).spread("Bar").array()); //[ 'B', 'a', 'r' ]

function TestSpread() {
    return Array.prototype.reduce.call(arguments, function (acc, currvalue) {
        return acc + currvalue;
    }, 0);
}

console.log(ES6.spreadOperator(TestSpread).spread([1, 2, 3, 4, 5]).call()); //15

function Student(name, roll) {
    this.name = name;
    this.roll = roll;
}

console.log(ES6.spreadOperator(Student).spread(["Ariyan", 10]).new().name); //Ariyan

Polyfills

  • Symbol

    • for()
    • keyFor
    • @@hasInstance
    • @@isConcatSpreadable
    • @@iterator
    • @@toStringTag
    • Symbol.prototype.toString()
    • Symbol.prototype.valueOf()
  • Function

    • Function.prototype[@@hasInstance]()
  • Array

    • Array.prototype.concat() (ES6 version, addition of @@isConcatSpreadable support)
    • Array.prototype[@@iterator]()
    • Array.from()
    • Array.prototype.entries()
    • Array.prototype.keys()
  • Object

    • Object.prototype.toString() (ES6 version, addition of @@toStringTag support)
  • String

    • String.prototype[@@iterator]()

Limitation

Some ES6 features can't be implemented in ES5 natively like spread operator, for..of loop, ES6 version of instanceOf operator etc. So this module exports a object named ES6 globally, that provides some approximate equivalent implementation of those features.

ES6 Object

This object provides,

  • isSymbol() (It can be used as equivalent API of: typeof symbol === 'symbol')
  • instanceOf() (Provides ES6 version of instanceOf)
  • forOf() (This method behaves exactly same as ES6 for...of loop)
  • spreadOperator (Gives same functionality of the spread operator of ES6)

Contributing

Your PRs and stars are always welcome.

Please, try to follow:

  • Clone the repository.
  • Checkout develop branch.
  • Install dependencies.
  • Add your new features or fixes.
  • Build the project.
$ git clone https://github.com/rousan/symbol-es6.git
$ cd symbol-es6
$ git checkout develop
$ npm i
$ npm run build