ES12 新特性

逻辑赋值操作符

• 逻辑赋值操作符将逻辑操作(&&、|| 或 ??)与赋值表达式组合在一起。

1. 带有 || 的逻辑赋值操作

let x = 0
let y = 1

x ||= y;
console.log(x)  // 1
console.log(y)  // 1

let x = 1
let y = 2

x ||= y;
console.log(x)  // 1
console.log(y)  // 2

<!-- 等价于 -->
x || (x = y)

<!-- 或者等价于 -->
if (x) {
  x = y
}

2. 带有 && 的逻辑赋值操作

let x = 1
let y = 2

x &&= y
console.log(x) // 2
console.log(y) // 2

let x = 0
let y = 2

x &&= y
console.log(x) // 0
console.log(y) // 2

3. 带有 ?? 的逻辑赋值操作符

let x
let y = 2

x ??= y
console.log(x) // 2

let x = 1
let y = 2

x ??= y
console.log(x) // 1

数字分隔符，只是为了增加可读性，所以可以放在数字内的任何地方

const num = 100_000_000
console.log(num) // 100000000

const num_f = 100_000_000.123456
console.log(num_f) // 100000000.123456

const num_2 = 0b101001
console.log(num_2) // 41

const numbig = 100_000_000_000n
console.log(numbig) // 100000000000n
console.log(numbig.toString()) // 100000000000

Promise.any 与 AggregateError

• Promise.any()返回第一个完成的promise的值
• 如果所有传递给Promise.any()作为参数(作为数组)的Promise都被拒绝，则抛出一个"AggregateError"异常。

const p1 = new Promise((resolve, reject) => {
  setTimeout(() => resolve('A'), Math.floor(Math.random() * 1000))
})

const p2 = new Promise((resolve, reject) => {
  setTimeout(() => resolve('B'), Math.floor(Math.random() * 1000))
})

const p3 = new Promise((resolve, reject) => {
  setTimeout(() => resolve('C'), Math.floor(Math.random() * 1000))
});

(async function() {
  const result = await Promise.any([p1, p2, p3]);
  console.log(result)
})();  // A 或 B 或 C

const p = new Promise((resolve ,reject) => reject());

try {
  (async function() {
    const result = await Promise.any([p])
    console.log(result)
  })();
} catch(error) {
  console.log(error)  // Uncaught (in promise) AggregateError: All promises were rejected
}

String.prototype.replaceAll 方法

• String.prototype.replaceAll()允许我们用一个不同的值替换字符串中的所有子串实例，而不需要使用全局正则表达式。

const str = "Backbencher sits at the Back"
const newstr = str.replaceAll("Back", "Front")
const newstr1 = str.replace(/Back/g, "Front")
const newstr2 = str.replace("Back", "Front")
console.log(newstr)  // Frontbencher sits at the Front
console.log(newstr1) // Frontbencher sits at the Front
console.log(newstr2) // Frontbencher sits at the Back