解构赋值 - 对象的解构赋值

        let { baz } = { foo: ‘aaa‘, bar: ‘bbb‘ };
        console.log(baz)  // undefined

        let obj = { first: ‘hello‘, last: ‘world‘ };
        let { first: f, last: l } = obj;
        console.log(f) // ‘hello‘
        console.log(l) // ‘world‘

        var { x: yy = 3 } = {};
        var { x: y = 3 } = { x: 5 };
        console.log(yy) // 3
        console.log(y) // 5