ES6 - ECMA2018 - 学习总结

新的概念与方法

概略图：

ECMA2018

基本使用

rest操作符解构赋值

1. 合并数组

const [...iterableObj] = [1, 3, 5, 7, 9];
let newArr = [...iterableObj, 0, 2, 4, 6, 8];
console.log(newArr);  //Array(10) [ 1, 3, 5, 7, 9, 0, 2, 4, 6, 8 ]

2. 合并对象

let obj = { foo: 10, bar: 20, baz: 30 };
let {foo, ...rest} = obj;
console.log(foo);  // 10
console.log(rest);  // Object { bar: 2, baz: 3 }

const DEFAULTS = {foo: 'a', bar: 'b'};
const userData = {foo: 1};
const data = {...DEFAULTS, ...userData};
console.log(data);  // {foo: 1, bar: 'b'}

正则扩展 具名分组

const RE_DATE = /([0-9]{4})-([0-9]{2})-([0-9]{2})/;
let matchObj = RE_DATE.exec('1999-12-31');
let year = matchObj[1]; // 1999
let month = matchObj[2]; // 12
let day = matchObj[3]; // 31

Promise 扩展方法finally， 继then、catch之后 第三个阶段函数

finally回掉会一直执行，不像then与catch只可以逻辑二选一
Promise.prototype.finally()

let connection;
db.open()
.then(conn => {
    connection = conn;
    return connection.select({ name: 'Jane' });
})
.then(result => {
    // Process result
    // Use `connection` to make more queries
})
···
.catch(error => {
    // handle errors
})
.finally(() => {
    connection.close();
});

for await...of

异步生成器已经实现了异步迭代器协议, 所以可以用 for await...of循环

async function* asyncGenerator() {
  var i = 0;
  while (i < 3) {
    yield i++;
  }
}

(async function() {
  for await (num of asyncGenerator()) {
    console.log(num);
  }
})();