数组的结构赋值
按顺序排列，取值由位置决定
let [a, b, c] = [1, 2, 3]
a //1
b //2
c //3
let [x, y, ...z] = ['a'];
x // a
y //undefined 结构不成功
z //[]
let [e, f, g] = [1, [2, 3], 4];
e //1
f //2 不完全结构
g //4
let [foo] = 1;//报错，右边等号的值或者转为对象以后必须具备Iterator接口
let [f = true] = [];
f //true 默认值
对象的机构赋值
变量名与属性名必须相同才能取值，先找到同名属性，在赋值给对应的变量，真正被复制的是变量
let {bar, foo} = {
foo: "aaa",
bar: "bbb"
};
bar //bbb
foo //aaa
let baz = {
foo: "aaa",
bar: "bbb"
};
baz //undefined
var {foo: baz} = {
foo: "aaa",
bar: "bbb"
};
baz // aaa
嵌套赋值
let obj = {
p: [
"hello",
{y: 'world'}
]
};
let {p: [x, {y}]} = obj;
x //hello
y //world
let {p, {p: [x, {y}]}} = obj;
x //hello
y //world
p //["hello", {y: "world"}]
默认赋值
必须严格等于undefined，结构赋值失败值等于undefined
其他
子串会被解析为一个类数组
let [a, c] = "ad";
a //"a"
c //"d"
布尔与数字的结构赋值
等号做组边是数字或者布尔是，会先转换为对象。null和undefined无法转换为对象，报错
let {to: s} = 123;
s// undefined Number 沒有to方法
let {toString: ss} = 123;
ss //toString() { [native code] }
//ss === Number.prototype.toString true
// s === Number.prototype.toString false
let {prop: x} = undefined; // TypeError
用途
1、交互变量
let x = 1, y = 2;
[x, y] === [y, x];
x //2
y //1
2、读取函数返回值
function fn(){
return [1, 2, 3];
}
let [a, b, c] = fn();
function fn1(){
return {
foo: 1,
bar: 2
}
}
let {foo, bar} = fn1();
foo //1
bar //2
