esnext —— 将 ES6 转成 JavaScript 代码

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 code
re-written so it can run in today's browsers.

Edits made to the code on the left will re-generate and
re-run the code on the right. Try it out!
*/

// Classes
class 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 functions
console.log([1, 2, 3].map(x => x * x));

// Rest params
function join(delim, ...items) {
  return items.join(delim);
}

// Spread args
console.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 code
re-written so it can run in today's browsers.

Edits made to the code on the left will re-generate and
re-run the code on the right. Try it out!
*/

// Classes
var $__Array$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 functions
console.log([1, 2, 3].map(function(x) {
  return x * x;
}));

// Rest params
function join(delim) {
  var $__arguments = arguments;
  var items = [].slice.call($__arguments, 1);
  return items.join(delim);
}

// Spread args
console.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 [http://www.oschina.net]