ES2022 有什么新功能？

新版本的 ECMA Script 将在几个月内成为标准。那么让我们来看看将成为 ES2022 一部分的特性

1..at()可索引值的方法

这个函数让我们读取给定索引处的元素。它可以接受负索引来从给定数据类型的末尾读取元素

[1,2,3,4,5].at(3)  // 4

[1,2,3,4,5].at(-2)   // 4

支持此功能的数据类型

• String
• Array
• All Typed Array classes: Uint8Array etc.

2.RegExp 匹配索引

/d向正则表达式添加标志会生成匹配对象，记录每个组捕获的开始和结束

有不同的方法来匹配索引

const matchObj = /(a+)(b+)/d.exec('aaaabb');

console.log(matchObj);
/*
Output -
['aaaabb', 'aaaa', 'bb', index: 0, input: 'aaaabb', groups: undefined, indices: Array(3)]
*/

matchObj.indices[1];
/*
Output - 
[0, 4]
*/

const matchObj = /(?<as>a+)(?<bs>b+)/d.exec('aaaabb');

console.log(matchObj);
/*
Output - 
['aaaabb', 'aaaa', 'bb', index: 0, input: 'aaaabb', groups: {as: 'aaaa', bs: 'bb'}, indices: Array(3)]
*/

matchObj.indices.groups;
/*
Output -
{ as: [0,4], bs: [4,6] }
*/

3.Object.hasOwn(obj, propKey)

这是检查propKey对象自身属性的一种安全方法obj。它类似于Object.prototype.hasOwnProperty但它支持所有对象类型

const proto = {
  protoProp: 'protoProp',
};

const obj = {
  __proto__: proto,
  objProp: 'objProp',
};

console.log('protoProp' in obj); // output - true.
console.log(Object.hasOwn(obj, 'protoProp')) // output - false
console.log(Object.hasOwn(proto, 'protoProp')); // output - true.

4.error.cause

错误及其子类现在让我们指定错误背后的原因。这在深度嵌套函数中很有用，我们将错误块链接起来以快速找到错误

function readFiles(filePaths) {
  return filePaths.map(
    (filePath) => {
      try {
        // ···
      } catch (error) {
        throw new Error(
          `While processing ${filePath}`,
          {cause: error}
        );
      }
    });
}

5.顶层等待模块

动态加载模块

const messages = await import(`./messages-${language}.mjs`);

如果模块加载失败，使用回退

let lodash;
try {
  lodash = await import('https://primary.example.com/lodash');
} catch {
  lodash = await import('https://secondary.example.com/lodash');
}

使用加载速度最快的资源

const resource = await Promise.any([
  fetch('http://example.com/first.txt')
    .then(response => response.text()),
  fetch('http://example.com/second.txt')
    .then(response => response.text()),
]);

6.Class 新成员

Public

class InstPublicClass {
  // Instance public field
  instancePublicField = 0; // (A)

  constructor(value) {
    // We don’t need to mention .property elsewhere!
    this.property = value; // (B)
  }
}

const inst = new InstPublicClass('constrArg');

const computedFieldKey = Symbol('computedFieldKey');
class StaticPublicFieldClass {
  static identifierFieldKey = 1;
  static 'quoted field key' = 2;
  static [computedFieldKey] = 3;
}
console.log(StaticPublicFieldClass.identifierFieldKey) //output -> 1
console.log(StaticPublicFieldClass['quoted field key']) //output -> 2
console.log(StaticPublicFieldClass[computedFieldKey]) //output -> 3

Private

class InstPrivateClass {
  #privateField1 = 'private field 1'; // (A)
  #privateField2; // (B) required!
  constructor(value) {
    this.#privateField2 = value; // (C)
  }
  /**
   * Private fields are not accessible outside the class body.
   */
  checkPrivateValues() {
  console.log(this.#privateField1); // output -> 'private field 1'
  console.log(this.#privateField2); // output -> 'constructor argument'

  }
}

const inst = new InstPrivateClass('constructor argument');
  inst.checkPrivateValues();


console.log("inst", Object.keys(inst).length === 0) //output -> inst, true

class InstPrivateClass {
  #privateField1 = 'private field 1'; // (A)
  #privateField2; // (B) required!
  static #staticPrivateField = 'hello';
  constructor(value) {
    this.#privateField2 = value; // (C)
  }
  /**
   * Private fields are not accessible outside the class body.
   */
  checkPrivateValues() {
    console.log(this.#privateField1); // output -> 'private field 1'
    console.log(this.#privateField2); // output -> 'constructor argument'

  }

  static #twice() {
    return this.#staticPrivateField + " " + this.#staticPrivateField;
  }

  static getResultTwice() {
    return this.#twice()
  }
}

const inst = new InstPrivateClass('constructor argument');
inst.checkPrivateValues();


console.log("inst", Object.keys(inst).length === 0) //output -> "inst", true
console.log(InstPrivateClass.getResultTwice()); // output -> "hello hello"

class MyClass {
  #privateMethod() {}
  static check() {
    const inst = new MyClass();

    console.log(#privateMethod in inst) // output-> true

    console.log(#privateMethod in MyClass.prototype) // output-> false

    console.log(#privateMethod in MyClass) // output-> false
  }
}
MyClass.check();

class Translator {
  static translations = {
    yes: 'ja',
    no: 'nein',
    maybe: 'vielleicht',
  };
  static englishWords = [];
  static germanWords = [];
  static { // (A)
    for (const [english, german] of Object.entries(this.translations)) {
      this.englishWords.push(english);
      this.germanWords.push(german);
    }
  }
}


console.log(Translator.englishWords, Translator.germanWords)
//Output -> ["yes", "no", "maybe"], ["ja", "nein", "vielleicht"]

class C1 {
  #priv() {}
  static check(obj) {
    return #priv in obj;
  }
}

console.log(C1.check(new C1())) // output true

这些功能将帮助我们增强我们的项目并改进我们的编码技术。我很高兴能在我的项目中尝试这些功能