Array Destructuring Assignment

old school

const items = [1, 2, 3];
const item1 = items[0];
const item2 = items[1];
const item3 = items[2];

一個一個從 array 拿出來, 再一個一個 assign 給每一個變數.

modern

const [item1, item2, item3] = [1, 2, 3];

一行裡面做了 declare, assign, read from array. 3 個動作一氣呵成.

get someone

const [, , value3] = [1, 2, 3];

with default value

const [v1] = []; // v1 = undefined
const [v1 = 'default value'] = []; // v1 = 'default value'
const [v1 = 'default value'] = ['value']; // v1 = 'value'

Object Destructuring Assignment

它和 Array 的用法差不多.

const person = { name: 'Derrick', age: 11 };
const { name, age } = person;

with alias 別名

const person = { name: 'Derrick', age: 11 };
const { name: newName, age: newAge } = person;
console.log(newName);
console.log(newAge);

name: newName 中間使用了分號

with default value

const { name = 'Derrick', age } = {};
// name = 'Derrick'
// age = undefined