ECMAScript 6（ ES6）： JavaScript 的下一个版本有什么新东西（一）

if(true) {
    let x = 1;}
     console.log(x); // undefined

for(let i = 0, l = list.length; i < l; i++) {
      // do something with list[i]}
    console.log(i); // undefined

const MY_CONSTANT = 1;
    MY_CONSTANT = 2 // Error
    const SOME_CONST; // Error

const MY_OBJECT = {some: 1};
    MY_OBJECT.some = 'body'; // Cool

let books = [{title: 'X', price: 10}, {title: 'Y', price: 15}];
    let titles = books.map( item => item.title );
    // ES5 equivalent:var titles = books.map(function(item) {
      return item.title;
            });

// No argumentsbooks.map( () => 1 ); // [1, 1]
    // Multiple arguments[1,2].map( (n, index) => n * index ); // [0, 2]

let result = [1, 2, 3, 4, 5].map( n => {
    n = n % 3;
    return n;
            });

let book = {
     title: 'X',
     sellers: ['A', 'B'],
    printSellers() {
       this.sellers.forEach(seller => console.log(seller + ' sells ' + this.title));
       }}
    // ES5 equivalent:var book = {
    title: 'X',
    sellers: ['A', 'B'],
    printSellers: function() {
    var that = this;
    this.sellers.forEach(function(seller) {
    console.log(seller + ' sells ' + that.title)
       })
     }
            }