在ES6中按照一定模式，从数组和对象中提取值对变量进行赋值，这被称为解构（Destructuring）
-
以前，为变量赋值，只能直接指定值
let a = 'a'; let b = 'b'; let c = 'c'; -
ES6 允许写成下面这样
let [a, b, c] = ['a', 'b', 'c'] console.log(a); //a console.log(c); //c
这表示，可以从数组中提取值，按照对应位置，对变量赋值
举几个🌰
let [a,[[b],c]] = [1,[[2],3]] console.log(a); //1 console.log(b); //2 console.log(c); //3let [, , thrid] = ['first', 'second', 'thrid'] console.log(thrid);//thridlet [a, , c] = [1, 2, 3]; console.log(a); //1 console.log(c); //3let [a, ...b] = [1, 2, 3, 4] console.log(a); // 1 console.log(b); // [2,3,4]const [a, b, ...c] = ['a']; console.log(a); // a console.log(b); // undefined console.log(c); // []
如果解构不成功，变量值就是undefined
let [a] = [];
let [b, c] = [1];
console.log(a); // undefined
console.log(b); // 1
console.log(c); // undefined
或者是不完全解构，就是等号左边的模式，只匹配一部分等号右边的数组，这种情况是可以解构成功
let [x, y] = [1, 2, 3];
console.log(x); //1
console.log(y); //2
let [a, [b], d] = [1, [2, 3], 4]
console.log(a); //1
console.log(b); //2
console.log(d); //4
如果等号右边不是可以遍历的解构（不具有Iterator接口），就会报错
//以下全部报错
let [a] = 1;
let [a] = false;
let [a] = NaN;
let [a] = undefined;
let [a] = null;
let [a] = {};
Set结构，也可以使用数组的解构赋值
let [a, b, c] = new Set(['a', 'b', 'c'])
console.log(b); // b
事实上，只要数据结构具有Iterator接口，都可以采用数组形式进行结构赋值.
//fibs是一个Generator函数，原生具有Iterator接口
function* fibs() {
let [a, b] = [0, 1];
while (true) {
yield a;
[a, b] = [b, a + b]
}
}
let [first, second, thrid, fourth, fifth, sixth] = fibs();
console.log(first); // 0
console.log(sixth); // 5