es6 解構賦值

結構賦值即按照一種模式對變數進行賦值，分為數組解構賦值和對象結構賦值

1. 數組結構賦值

let a;
[a,b]=[1,2]//數組類型解構賦值
console.log(a);//1


[a,b,...rest]=[1,2,3,4,5,6]//輸出1,2,[3,4,5,6]


[a,b,c=3]=[1,2] //a=1,b=2,c=3

[a,b,c]=[1,2]//若左右沒有配對成功，則會輸出undefined。即c為undefined


let a=1;
let b=2;
[a,b]=[b,a];//可以進行交換，輸出2,1


function f(){
    return [1,2]
}
let a,b;
[a,b]=f();//輸出1,2


function f(){
    return [1,2,3,4,5]
}
let a,b,c;
[a,,,b]=f();//a,b輸出1,4


function f(){
    return [1,2,3,4,5]
}
let a,b,c;
[a,...b]=f();//a,b輸出1,[2,3,4,5]

2.對象解構賦值

let o={p:42,q:true} 
let {p,q}=o;//對象解構賦值左右都是對象
console.log(p,q);//42,true


let {a=10,b=5}={a:3};
console.log(a,b);//3,5


let metaData={
    title:"abc",
    test:[{
        title:"test",
        desc:"description"
    }]
}
let {title:esTitle,test:[{title:cnTitle}]}=metaData;
console.log(esTitle,cnTitle);//輸出abc,test