数组的解构赋值

• 如果匹配不到,则变量是undefined
• 如果等号右边不是数组(不可遍历的结构一包括对象),报错

{
    let arr = [10,20,30]
    let [a,b,c] = arr;
    console.log(a,b,c) //10,20,30
}
{
    /**默认值 */
    let [a=true] = [];
    console.log(a) //true
}
{
    /*数组解构赋值 */
    let [a,b,...c] = [1,2,3,4,5,6,7]
    console.log(a) //1
    console.log(b) //2
    console.log(c) //[3,4,5,6,7]
}

---

对象的解构赋值

如果匹配不到,则变量是Undefined

{
    let {aoo:ooo} = {aoo:'aaa',brr:'bbb'}
    //aoo是匹配模式
    //ooo是变量
    console.log(ooo) //aaa
}
{
    /**模式匹配用例 */
    let obj ={
        arr:[
            '111',
            {brr:222}
        ]
    };
    let {arr,arr:[x,{brr}]} = obj
    console.log(arr,x,brr) 
}
{
    /**默认值生效的条件是,对象的属性值严格等于undefined*/
    let {a=true} = {a:undefined}
    console.log(a) //true
}

---

字符串解构赋值

类似于数组的对象都有一个length属性,可以对这个属性解构赋值

{
    let [a,b,c] = "hello"
    console.log(a,b,c); // h e l
    let {length:len} = "hello"
    console.log(len) //5
}

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数值和布尔值的解构赋值

如果等号右边是数值和布尔值,则会先转为对象

{
    let {toString:s} = 123
    console.log(s)
}

---

函数的解构赋值

应用场景

{
    function test (){
        return [1,2]
    }
    let a,b;
    [a,b] = test()
    console.log(a,b)
}