解构的运用

let { bar, foo } = { foo: ‘aaa‘, bar: ‘bbb‘ };
foo // "aaa"
bar // "bbb"

let { ba } = { foo: ‘aaa‘, bar: ‘bbb‘ };
ba // undefined

let { foo: ba } = { foo: ‘aaa‘, bar: ‘bbb‘ };
ba // "aaa"
foo // error: foo is not defined

var {x = 3} = {};
x // 3

var {x, y = 5} = {x: 1};
x // 1
y // 5

var {x: y = 3} = {};
y // 3

var {x: y = 3} = {x: 5};
y // 5

var { message: msg = ‘Something went wrong‘ } = {};
msg // "Something went wrong"

var {x = 3} = {x: undefined};
x // 3

var {x = 3} = {x: null};
x // null

let arr = [1, 2, 3];
let {0 : first, [arr.length - 1] : last} = arr;
first // 1
last // 3