What is ES6?

6th Edition - ECMAScript 2015
https://en.wikipedia.org/wiki/ECMAScript#6th_Edition_-_ECMAScript_2015

ECMA-262
http://www.ecma-international.org/publications/standards/Ecma-262.htm

Compatibility tables
http://kangax.github.io/compat-table/es6/

Can I use ES6
https://caniuse.com/#search=es6

ECMAScript 6: Feature Overview & Comparison
http://es6-features.org/

let, const

let: Declare a variable with block scope
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let

const: Declare a constant variable with block scope
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const

never use var

jshint option varstmt
http://jshint.com/docs/options/#varstmt

Classes

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes
• syntactical sugar
• constructor
• extends
• super
• static method

Module

<script type="module" src="js/demo.js"></script>
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-type

<script nomodule src="js/demo-iife.js"></script>
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-nomodule

Fallback
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#Module_Fallback

import
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import

export
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/export

More features

Arrow functions
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions

Template literals
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

Default parameters
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters

Rest parameters
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters

Spread syntax
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax

Promises
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises

Destructuring assignment
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment

Enhanced Object literals
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Grammar_and_types#Enhanced_Object_literals

ES6 是 ECMAScript 6.0 的简写，即 JavaScript 语言的下一代标准，已经在 2015年6月正式发布了，它的目标是让JS能够方便的开发企业级大型应用程序，因此，ES6的一些规范正在逐渐向Java、C# 等后端语言标准靠近。在 ES6 规范中，比较重大的变化有以下几个方面：

新增 let、const 命令 来声明变量，和var 相比，let 声明的变量不存在变量提升问题，但没有改变JS弱类型的特点，依然可以接受任意类型变量的声明；const 声明的变量不允许在后续逻辑中改变，提高了JS语法的严谨性。
新增解构赋值、rest 语法、箭头函数等，这些都是为了让代码看起来更简洁，而包装的语法糖。
新增模块化机制，这是 JavaScript 走向规范比较重要的一步，让前端更方便的实现工程化。
新增类和继承的概念，配合模块化，JavaScript 也可以实现高复用、高扩展的系统架构。
新增模板字符串功能，高效简洁，结束拼接字符串的时代。
新增 Promise 机制，解决异步回调多层嵌套的问题。