ES6作用域和解构赋值

ES6 强制开启严格模式

作用域

• var 声明局部变量，for/if花括号中定义的变量在花括号外也可访问
• let 声明的变量为块作用域，变量不可重复定义
• const 声明常量，块作用域，声明时必须赋值，不可修改

// const声明的k指向一个对象，k本身不可变，但对象可变function test() {    const k={        a:1    }    k.b=3;    console.log(k);}test()

解构赋值

{    let a, b, 3, rest;    [a, b, c=3]=[1, 2];    console.log(a, b);}//output: 1 2 3{    let a, b, 3, rest;    [a, b, c]=[1, 2];    console.log(a, b);}//output: 1 2 undefined{    let a, b, rest;    [a, b, ...rest] = [1, 2, 3, 4, 5, 6];    console.log(a, b, rest);}//output:1 2 [3, 4, 5, 6]{    let a, b;    ({a, b} = {a:1, b:2})    console.log(a ,b);}//output: 1 2

使用场景

变量交换

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

获取多个函数值

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

获取多个函数返回值

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

对象解构赋值

{    let o={p:42, q:true};    let {p, q, c=5} = o;    console.log(p ,q);}//output: 42 true 5

获取json值

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