ES6 变量的解构赋值

1.数组的解构赋值

let [x = 1, y = x] = [];     // x=1; y=1
let [x = 1, y = x] = [2];    // x=2; y=2
let [x = 1, y = x] = [1, 2]; // x=1; y=2
let [x = y, y = 1] = [];     // ReferenceError

2.对象的解构赋值

var { foo: foo, bar: bar } = { foo: "aaa", bar: "bbb" };

var { foo: baz } = { foo: "aaa", bar: "bbb" };
baz // "aaa"
foo // error: foo is not defined

let foo;
let {foo} = {foo: 1}; // SyntaxError: Duplicate declaration "foo"

let baz;
let {bar: baz} = {bar: 1}; // SyntaxError: Duplicate declaration "baz"