ES6 Support: rename docs/es6-chromium.md -> docs/es6_chromium.md

docs/es6-chromium.md

-<!-- This is feature markdown template
-## Header
-
-**Usage Example:**
-
-``` js
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-```
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-**Documentation:** [link]()
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-[TOC]
-
-# ES6 Support In Chromium
-
-This is a list of new/updated features in ES6 specs that is being considered to
-be supported for Chromium development.
-
->**TBD:** Do we want to differenciate allow/ban status between subprojects? If
-so, how to denote?
-
->**TBD:** Cross platform-build support?
-
-You can propose changing the status of a feature by sending an email to
-chromium-dev@chromium.org. Include a short blurb on what the feature is and why
-you think it should or should not be allowed, along with links to any relevant
-previous discussion. If the list arrives at some consensus, send a codereview
-to change this file accordingly, linking to your discussion thread.
-
->Some descriptions and Usage examples are from [kangax](https://kangax.github.
-io/compat-table/es6/) and [http://es6-features.org/](http://es6-features.org/)
-
-# Allowed Features
-
-The following features are allowed in Chromium development.
-
-## `Promise`
-
-Built-in representation of a value that might be determined asynchronously,
-relieving developers from "callback hell".
-
-**Usage Example:**
-
-``` js
-function promiseA() {
-  return new Promise((resolve, reject) => setTimeout(resolve, 100));
-}
-
-function promiseB() {
-  return new Promise((resolve, reject) => setTimeout(resolve, 200));
-}
-
-function promiseC() {
-  return new Promise((resolve, reject) => setTimeout(resolve, 300));
-}
-
-Promise.all([promiseA(), promiseB(), promiseC()]).then(([a, b, c]) => {
-  someFunction(a, b, c);
-});
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-promise-objects)
-
-**Discussion Notes:** Feature already extensively used prior to creation of
-this document.
-
----
-
-# Banned Features
-
-The following features are banned for Chromium development.
-
-# Features To Be Discussed
-
-The following features are currently disallowed. See the top of this page on
-how to propose moving a feature from this list into the allowed or banned
-sections.
-
-## `let` (Block-Scoped Variables)
-
-Declare variable that exists within the block scope. `let` can generally be
-used to replace `var` but `let` in global scope, unlike `var`, does not
-introduce a property on the global object.
-
-**Usage Example:**
-
-``` js
-// This will make all buttons output "3".
-for(var i = 0; i < 3; i++) {
-  buttons[i].onclick = function() {
-    console.log(i);
-  };
-}
-
-// This will make buttons output corresponding "i" values.
-for(let i = 0; i < 3; i++) {
-  buttons[i].onclick = function() {
-    console.log(i);
-  };
-}
-
-var bar = 1;
-var bar = 1; // No error thrown.
-
-let foo = 1;
-let foo = 1; // TypeError: Identifier 'foo' has already been declared.
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-let-and-const-declarations)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `const` (Block-Scoped Constants)
-
-Constants (also known as "immutable variables") are variables which cannot be
-re-assigned new content. Note that if the value is an object, the object itself
-is still mutable.
-
-`const` has traditionally been supported as a "function scoped" declaration
-like `var` (except in Internet Explorer), however in VMs supporting ES6 `const`
-is now a block scope declaration.
-
-**Usage Example:**
-
-``` js
-const gravity = 9.81;
-gravity = 0; // TypeError: Assignment to constant variable.
-
-gravity === 9.81; // true
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-let-and-const-declarations)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `=>` (Arrow Functions)
-
-Arrow functions provide a concise syntax to create a function, and fix a number
-of difficulties with this (e.g. eliminating the need to write `const self =
-this`. Particularly useful for nested functions or callbacks.
-
-Prefer arrow functions over the function keyword, over `f.bind(this)`, and
-especially over `goog.bind(f, this)`.
-
-Arrow functions has an implicit return when used without a body block.
-
-**Usage Example:**
-
-``` js
-// General usage, eliminating need for .bind(this).
-setTimeout(() => {
-  this.doSomething();
-}, 1000);  // no need for .bind(this) or const self = this.
-
-// Another example...
-window.addEventListener('scroll', (event) => {
-  this.doSomething(event);
-});  // no need for .bind(this) or const self = this.
-
-// Implicit return: returns the value if expression not inside a body block.
-() => 1 // returns 1
-() => {1} // returns undefined - body block does not implicitly return.
-() => {return 1;} // returns 1
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-arrow-function-definitions)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Classes
-
-OOP-style and boilerplate-free class syntax, including inheritance, super(),
-static members, and getters and setters.
-
-**Usage Example:**
-
-``` js
-class Rectangle extends Shape {
-  constructor(id, x, y, width, height) {
-    super(id, x, y);
-    this.width  = width;
-    this.height = height;
-  }
-  static defaultRectangle() {
-    return new Rectangle('default', 0, 0, 100, 100);
-  }
-  move(x, y) {
-    this.x = x;
-    this.y = y;
-  }
-};
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-class-definitions)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Block Scope Functions
-
-**Usage Example:**
-
-``` js
-{
-  function foo() {
-    return 1;
-  }
-  // foo() === 1
-  {
-    function foo() {
-      return 2;
-    }
-    // foo() === 2
-  }
-  // foo() === 1
-}
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-functiondeclarationinstantiation)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Default Function Parameters
-
-**Usage Example:**
-
-``` js
-function f(x, y = 7, z = 42) {
-  return x + y + z;
-}
-// f(1) === 50;
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-functiondeclarationinstantiation)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Rest Parameters
-
-Aggregation of function arguments into one Array variable.
-
-**Usage Example:**
-
-``` js
-function f(x, y, ...a) {
-  // for f(1, 2, 3, 4, 5)...
-    // x = 1, y = 2
-    // a = [3, 4, 5]
-}
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-function-definitions)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Spread Operators
-
-Spreading the elements from an iterable collection into individual literals as
-function parameters.
-
-**Usage Example:**
-
-``` js
-// Spreading an Array
-var params = [ 'hello', true, 7 ];
-var other = [ 1, 2, ...params ]; // [ 1, 2, 'hello', true, 7 ]
-f(1, 2, ...params) === 9;
-
-// Spreading a String
-var str = 'foo';
-var chars = [ ...str ]; // [ 'f', 'o', 'o' ]
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-argument-lists-runtime-semantics-argumentlistevaluation)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Object Literal Extensions
-
-Convenient new ways for object property definition.
-
-**Usage Example:**
-
-``` js
-// Computed property name
-var x = 'key';
-var obj = {[x]: 1};
-
-// Shorthand property
-var obj = {x, y}; //equivalent to {x:x, y:y}
-
-// Method property
-var obj = {
-  foo() {...},
-  bar() {...}
-}
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-object-initialiser)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Template Literals
-
-Expression interpolation for Strings, with the ability to access raw template
-pieces.
-
-**Usage Example:**
-
-``` js
-// Simple example
-var greeting = 'hello';
-var myName = {first: 'Foo', last: 'Bar'};
-var message = `${greeting},
-my name is ${myName.first + myName.last}`;
-// message == 'hello,\nmy name is FooBar'
-
-// Custom interpolation
-function foo (strings, ...values) {
-  // for foo`bar${42}baz`...
-    // strings[0] === 'bar';
-    // strings[1] === 'baz';
-    // values[0] === 42;
-
-  return strings[1] + strings[0] + values[0];
-}
-
-var newString = foo`bar${42}baz`; // 'bazbar42'
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-template-literals)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Binary & Octal Literals
-
-**Usage Example:**
-
-``` js
-0b111110111 === 503;
-0o767 === 503;
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-literals-numeric-literals)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `/u` Unicode Regex Literal
-
-**Usage Example:**
-
-``` js
-'𠮷'.match(/./u)[0].length === 2;
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-get-regexp.prototype.sticky)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `\u{}` Unicode String
-
-**Usage Example:**
-
-``` js
-'\u{1d306}' == '\ud834\udf06'; // true
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-literals-string-literals)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `/y` Regex Sticky Matching
-
-Keep the matching position sticky between matches and this way support
-efficient parsing of arbitrary long input strings, even with an arbitrary
-number of distinct regular expressions.
-
-**Usage Example:**
-
-``` js
-var re = new RegExp('yy', 'y');
-re.lastIndex = 3;
-var result = re.exec('xxxyyxx')[0];
-result === 'yy' && re.lastIndex === 5; // true
-```
-
-**Documentation:** [link](http://es6-features.org
-/#RegularExpressionStickyMatching)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Destructuring Assignment
-
-Flexible destructuring of collections or parameters.
-
-**Usage Example:**
-
-``` js
-// Array
-var list = [ 1, 2, 3 ];
-var [ a, , b ] = list;
-// a = 1, b = 3
-
-// Object
-var {width, height, area: a} = rect;
-// width = rect.width, height = rect.height, a = rect.area
-
-// Parameters
-function f ([ name, val ]) {
-  console.log(name, val);
-}
-function g ({ name: n, val: v }) {
-  console.log(n, v);
-}
-function h ({ name, val }) {
-  console.log(name, val);
-}
-
-f([ 'bar', 42 ]);
-g({ name: 'foo', val:  7 });
-h({ name: 'bar', val: 42 });
-
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-destructuring-assignment)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Modules
-
-Support for exporting/importing values from/to modules without global
-namespace pollution.
-
-**Usage Example:**
-
-``` js
-// lib/rect.js
-export function getArea() {...};
-export { width, height, unimportant };
-
-// app.js
-import {getArea, width, height} from 'lib/rect';
-
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-modules)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Symbol Type
-
-Unique and immutable data type to be used as an identifier for object
-properties.
-
-**Usage Example:**
-
-``` js
-const foo = Symbol();
-const bar = Symbol();
-typeof foo === 'symbol'; // true
-typeof bar === 'symbol'; // true
-let obj = {};
-obj[foo] = 'foo';
-obj[bar] = 'bar';
-JSON.stringify(obj); // {}
-Object.keys(obj); // []
-Object.getOwnPropertyNames(obj); // []
-Object.getOwnPropertySymbols(obj); // [ foo, bar ]
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-symbol-constructor)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `for ...of` Loops
-
-Convenient operator to iterate over all values of an iterable object.
-
-**Usage Example:**
-
-``` js
-// Given an iterable  collection `fibonacci`...
-for (let n of fibonacci) {
-  console.log(n);
-}
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-for-in-and-for-of-statements)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Object Static Methods
-
-**Usage Example:**
-
-``` js
-// Object.assign
-var o = Object.assign({a:true}, {b:true}, {c:true});
-'a' in o && 'b' in o && 'c' in o; // true
-
-// Object.setPrototypeOf
-Object.setPrototypeOf({}, Array.prototype) instanceof Array; //true
-
-// Object.is
-// Object.getOwnPropertySymbols
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-properties-of-the-object-constructor)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## String Static & Prototype methods
-
-**Usage Example:**
-
-``` js
-// String.raw
-// String.fromCodePoint
-
-// String.prototype.codePointAt
-// String.prototype.normalize
-// String.prototype.repeat
-// String.prototype.startsWith
-// String.prototype.endsWith
-// String.prototype.includes
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-properties-of-the-string-constructor)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Array Static & Prototype Methods
-
-**Usage Example:**
-
-``` js
-// Array.from
-// Array.of
-
-// Array.prototype.copyWithin
-// Array.prototype.find
-// Array.prototype.findIndex
-// Array.prototype.fill
-// Array.prototype.keys
-// Array.prototype.values
-// Array.prototype.entries
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-properties-of-the-array-constructor)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Number Properties
-
-**Usage Example:**
-
-``` js
-// Number.isFinite
-// Number.isInteger
-// Number.isSafeInteger
-// Number.isNaN
-// Number.EPSILON
-// Number.MIN_SAFE_INTEGER
-// Number.MAX_SAFE_INTEGER
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-isfinite-number)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Iterators
-
-**Usage Example:**
-
-``` js
-let fibonacci = {
-  [Symbol.iterator]() {
-    let pre = 0, cur = 1;
-    return {
-      next () {
-        [ pre, cur ] = [ cur, pre + cur ];
-        return { done: false, value: cur };
-      }
-    };
-  }
-};
-```
-
-**Documentation:** [link]()
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Generators
-
-Special iterators with specified pausing points.
-
-**Usage Example:**
-
-``` js
-function* range(start, end, step) {
-  while (start < end) {
-    yield start;
-    start += step;
-  }
-}
-
-for (let i of range(0, 10, 2)) {
-  console.log(i); // 0, 2, 4, 6, 8
-}
-
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-generator-function-definitions)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `Map`
-
-**Usage Example:**
-
-``` js
-var key = {};
-var map = new Map();
-
-map.set(key, 123);
-
-map.has(key) && map.get(key) === 123; // true
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-map-objects)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `Set`
-
-**Usage Example:**
-
-``` js
-var obj = {};
-var set = new Set();
-
-set.add(123);
-set.add(123);
-
-set.has(123); // true
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-set-objects)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `WeakMap`
-
-WeakMap does not prevent garbage collection if nothing else refers to an object
-within the collection.
-
-**Usage Example:**
-
-``` js
-var key = {};
-var weakmap = new WeakMap();
-
-weakmap.set(key, 123);
-
-weakmap.has(key) && weakmap.get(key) === 123; // true
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-weakmap-objects)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `WeakSet`
-
-WeakSet does not prevent garbage collection if nothing else refers to an object
-within the collection.
-
-**Usage Example:**
-
-``` js
-var obj1 = {};
-var weakset = new WeakSet();
-
-weakset.add(obj1);
-weakset.add(obj1);
-
-weakset.has(obj1); // true
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-weakset-objects)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Typed Arrays
-
-A lot of new typed Arrays...
-
-**Usage Example:**
-
-``` js
-new Int8Array();
-new UInt8Array();
-new UInt8ClampedArray()
-// ...You get the idea. Click on the Documentation link below to see all.
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-typedarray-objects)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `Proxy`
-
-Hooking into runtime-level object meta-operations.
-
-**Usage Example:**
-
-``` js
-let target = {
-  foo: 'Welcome, foo'
-};
-let proxy = new Proxy(target, {
-  get (receiver, name) {
-    return name in receiver ? receiver[name] : `Hello, ${name}`;
-  }
-});
-proxy.foo === 'Welcome, foo'; // true
-proxy.world === 'Hello, world'; // true
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-proxy-object-internal-methods-and-internal-slots)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## `Reflection`
-
-Make calls corresponding to the object meta-operations.
-
-**Usage Example:**
-
-``` js
-let obj = { a: 1 };
-Object.defineProperty(obj, 'b', { value: 2 });
-obj[Symbol('c')] = 3;
-Reflect.ownKeys(obj); // ['a', 'b', Symbol(c)]
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-reflection)
-
-**Discussion Notes / Link to Thread:**
-
----
-
-## Math Methods
-
-A lot of new Math methods.
-
-**Usage Example:**
-
-``` js
-// See Doc
-```
-
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-math)
-
-**Discussion Notes / Link to Thread:**
-
----