esnext 是一个 JavaScript 库，可以将 ES6 草案规范语法转成今天的 JavaScript 语法。

例如：

/*On the left is code written with new JavaScript features,and on the right is the console output, plus the same codere-written so it can run in today's browsers.Edits made to the code on the left will re-generate andre-run the code on the right. Try it out!*/// Classesclass Person {  constructor(firstName, lastName) {    this.firstName = firstName;    this.lastName = lastName;  }  get name() {    // Template strings    return `${this.firstName} ${this.lastName}`;  }  toString() {    return this.name;  }}console.log(  'Full name is:',  new Person('Michael', 'Bluth'));// Arrow functionsconsole.log([1, 2, 3].map(x => x * x));// Rest paramsfunction join(delim, ...items) {  return items.join(delim);}// Spread argsconsole.log(join('-', ...[415, 555, 1212]));

将被转换成：

/*On the left is code written with new JavaScript features,and on the right is the console output, plus the same codere-written so it can run in today's browsers.Edits made to the code on the left will re-generate andre-run the code on the right. Try it out!*/// Classesvar $__Array$prototype$slice = Array.prototype.slice;var $__Object$defineProperties = Object.defineProperties;var Person = function() {  "use strict";  function Person(firstName, lastName) {    this.firstName = firstName;    this.lastName = lastName;  }  $__Object$defineProperties(Person.prototype, {    name: {      get: function() {        // Template strings        return "" + this.firstName + " " + this.lastName + "";      },      enumerable: true,      configurable: true    },    toString: {      value: function() {        return this.name;      },      enumerable: false,      writable: true    }  });  $__Object$defineProperties(Person, {});  return Person;}();console.log(  'Full name is:',  new Person('Michael', 'Bluth'));// Arrow functionsconsole.log([1, 2, 3].map(function(x) {  return x * x;}));// Rest paramsfunction join(delim) {  var $__arguments = arguments;  var items = [].slice.call($__arguments, 1);  return items.join(delim);}// Spread argsconsole.log(join.apply(null, ['-'].concat($__Array$prototype$slice.call([415, 555, 1212]))));

使用方法：

var transpiler = require('es6-module-transpiler');var Container = transpiler.Container;var FileResolver = transpiler.FileResolver;var BundleFormatter = transpiler.formatters.bundle;var container = new Container({  resolvers: [new FileResolver(['lib/'])],  formatter: new BundleFormatter()});container.getModule('index');container.write('out/mylib.js');

文章转载自 开源中国社区 [