留下 4 分钟,本篇带你快速过一遍 ES12 的 5 个要点!!
1. 数字分隔符
数字分隔符是数字之间添加的下划线,这使得数字更可读;当代码解析时,下划线会被自动去除;
举栗🌰
// 十进制数字,按照千位进行划分
let n1 = 1_000_000_000;
console.log(n1); // This will print: 1000000000
// 十进制数字,按照千位进行划分,带小数点
let n2 = 1_000_000_000.150_200
console.log(n2); // This will print: 1000000000.1502
// 十六进制数字,按照字节分组
let n3 = 0x95_65_98_FA_A9
console.log(n3); // This will print: 641654651561
// 大文字,按千位划分
let n4 = 155_326_458_156_248_168_514n
console.log(n4); // This will print: 155326458156248168514n
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2. replaceAll
我们之前是 "abca".repalce(/a/g,"a1")
这样写正则的方式实现替换全部,现在直接用 replaceAll()
就可以了~
举栗🌰
// 声明一个字符串
const orgStr = 'JavaScript, often abbreviated as JS, is a programming language that conforms to the ECMAScript specification. JavaScript is high-level, often just-in-time compiled and multi-paradigm.';
// 用 replace 替换第一个选中元素
let newStr = orgStr.replace('JavaScript', 'TypeScript');
console.log(newStr);
// 用 replaceAll 替换所有选中元素
let newStr2 = orgStr.replaceAll('JavaScript', 'TypeScript');
console.log(newStr2);
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3. Promise.any()
Promise.any()
和 Promise.all()
相对:
前者是执行的 Promise 数组中,只要有其中一个 Promise resolve
(或全部 reject
) 则会进入 .then
(或 .catch
);
而后者是全部 Promise resolve
(或有一个 reject
),才会进入 .then
(或 .catch
)。
举栗🌰:任一 Promise resolve 即返回
// 创建 promise1
const promise1 = new Promise((resolve, reject) => {
// 2 秒后 resolve
setTimeout(() => resolve("The first promise has been resolved."), 2000);
});
// 创建 promise2
const promise2 = new Promise((resolve, reject) => {
// 1 秒后 resolve
setTimeout(() => resolve("The second promise has been resolved."), 1000);
});
// 创建 promise3
const promise3 = new Promise((resolve, reject) => {
// 3 秒后 resolve
setTimeout(() => resolve("The third promise has been resolved."), 3000);
});
(async function () {
const data = await Promise.any([promise1, promise2, promise3]);
// 第一个 resolve 后,立即返回给 data
console.log(data);
// 打印信息: The second promise has been resolved.
})();
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举栗🌰:全部 Promise reject 即返回
// 创建 promise1
const promise1 = new Promise((resolve, reject) => {
// After 1 second reject the first promise.
setTimeout(() => reject("The first promise has been rejected."), 1000);
});
// 创建 promise2
const promise2 = new Promise((resolve, reject) => {
// After 500 miliseconds reject the second promise.
setTimeout(() => reject("The second promise has been rejected."), 500);
});
// 立即执行
(async function () {
try {
const data = await Promise.any([promise1, promise2]);
console.log(data);
} catch (error) {
// 全部 Promise reject 则返回;
console.log("Error: ", error);
// 打印信息:Error: AggregateError: All promises were rejected
}
})();
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4. 三个逻辑赋值
ES12 引入了 3 个新的逻辑赋值运算符:
||=
逻辑或赋值,等同于:a || (a = b)
&&=
逻辑与赋值,等同于:a && (a = b)
??=
逻辑合并赋值,等同于:a ?? (a = b)
举栗🌰:||=
// 当 ||= 左侧的值是 false,则更改赋值为等号后的值
let myPlaylist = {songsCount: 0, songs:[]};
myPlaylist.songsCount ||= 100;
console.log(myPlaylist); // This will print: {songsCount: 100, songs: Array(0)}
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举栗🌰:&&=
// 当 &&= 左侧的值是 true,则更改赋值为等号后的值
let myFiles = {filesCount: 100, files:[]};
myFiles.filesCount &&= 5;
console.log(myFiles); // This will print: {filesCount: 5, files: Array(0)}
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举栗🌰:??=
// 当 ??= 左侧的值是 null or undefined,则更改赋值为等号后的值
let userDetails = {firstname: 'Katina', age: 24}
userDetails.lastname ??= 'Dawson';
console.log(userDetails); // This will print: {firstname: 'Katina', age: 24, lastname: 'Dawson'}
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5. 私有类方法/属性
Class 默认情况下类方法和属性都是公共的,在 ES12 中可以用 #
加一个前缀符号创建私有的方法和属性;
// 创建 User 类
class User {
constructor() {}
// 加 # 井号设为私有方法
#generateAPIKey() {
return "d8cf946093107898cb64963ab34be6b7e22662179a8ea48ca5603f8216748767";
}
getAPIKey() {
// 调用私有方法
return this.#generateAPIKey();
}
}
const user = new User();
const userAPIKey = user.getAPIKey();
console.log(userAPIKey); // This will print: d8cf946093107898cb64963ab34be6b7e22662179a8ea48ca5603f8216748767
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同时,类里面也可以设置私有的 Getter
和 Setter
;
// 创建 Str 类
class Str {
// 设置私有属性
#uniqueStr;
constructor() {}
// 私有 Setter
set #generateUniqueStringByCustomLength(length = 24) {
const characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
let randomStr = "";
for (let i = 0; i < length; i++) {
const randomNum = Math.floor(Math.random() * characters.length);
randomStr += characters[randomNum];
}
this.#uniqueStr = randomStr;
}
// 公共 Setter
set setRandomString(length) {
this.#generateUniqueStringByCustomLength = length;
}
// 私有 Getter
get #fetchUniqueString() {
return this.#uniqueStr;
}
// 公共 Getter
get getRandomString() {
return this.#fetchUniqueString;
}
}
const str = new Str();
// 调用公共 Setter,然后访问私有 Setter
str.setRandomString = 20;
// 调用公共 Getter,然后访问私有 Getter
const uniqueStr = str.getRandomString;
console.log(uniqueStr); // 每次在 Setter 之后执行 Getter ,将打印一个随机字符串
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OK,以上便是本篇分享,周末愉快 O(∩_∩)O,我是掘金安东尼,公众号同名,日拱一卒、日掘一金,再会~~
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