【JS】1394- ES2022 的 8 個(gè)實(shí)用的新功能

// ? a regex with a 'B' named group captureconst expr = /a+(?<B>b+)+c/d;
const result = expr.exec("aaabbbc")
// ? shows start-end matches + named group matchconsole.log(result.indices);// prints [Array(2), Array(2), groups: {…}]
// ? showing the named 'B' group matchconsole.log(result.indices.groups['B'])// prints [3, 6]

// users.jsexport const users = await fetch('/users/lists');
// usage.jsimport { users } from "./users.js";// ? the module will wait for users to be fullfilled prior to executing any codeconsole.log(users);

const array = [1,2,3,4,5,6]
// ? When used with positive index it is equal to [index]array.at(0) // 1array[0] // 1
// ? When used with negative index it mimicks the Python behaviourarray.at(-1) // 6array.at(-2) // 5array.at(-4) // 3

const array = [1,2,3,4,5,6];
// ? Different ways of accessing the third positionconst {3: third} = array; // third = 4array.at(3) // 4array[3] // 4

const x = { foo: "bar" };
// ? grabbing the hasOwnProperty function from prototypeconst hasOwnProperty = Object.prototype.hasOwnProperty
// ? executing it with the x contextif (hasOwnProperty.call(x, "foo")) {  ...}

const x = { foo: "bar" };
// ? using the new Object methodif (Object.hasOwn(x, "foo")) {  ...}

async function fetchUserPreferences() {  try {     const users = await fetch('//user/preferences')      .catch(err => {        // What is the best way to wrap the error?        // 1. throw new Error('Failed to fetch preferences ' + err.message);        // 2. const wrapErr = new Error('Failed to fetch preferences');        //    wrapErr.cause = err;        //    throw wrapErr;        // 3. class CustomError extends Error {        //      constructor(msg, cause) {        //        super(msg);        //        this.cause = cause;        //      }        //    }        //    throw new CustomError('Failed to fetch preferences', err);      })    }}
fetchUserPreferences();

async function fetcUserPreferences() {  try {     const users = await fetch('//user/preferences')      .catch(err => {        throw new Error('Failed to fetch user preferences, {cause: err});      })    }}
fetcUserPreferences();

class Foo {  #iteration = 0;
  increment() {    this.#iteration++;  }
  logIteration() {    console.log(this.#iteration);  }}
const x = new Foo();
// ? Uncaught SyntaxError: Private field '#iteration' must be declared in an enclosing classx.#iteration
// ? worksx.increment();
// ? worksx.logIteration();

class Foo {  #iteration = 0;
  #auditIncrement() {    console.log('auditing');  }
  increment() {    this.#iteration++;    this.#auditIncrement();  }}
const x = new Foo();
// ? Uncaught SyntaxError: Private field '#auditIncrement' must be declared in an enclosing classx.#auditIncrement
// ? worksx.increment();

// ? will output 'one two three'class A {  static {      console.log('one');  }  static {      console.log('two');  }  static {      console.log('three');  }}

let getPrivateField;
class A {  #privateField;  constructor(x) {    this.#privateField = x;  }  static {    // ? it can access any private field    getPrivateField = (a) => a.#privateField;  }}
const a = new A('foo');// ? Works, foo is printedconsole.log(getPrivateField(a));

class Foo {  #brand;
  static isFoo(obj) {    return #brand in obj;  }}
const x = new Foo();
// ? works, it returns trueFoo.isFoo(x);
// ? works, it returns falseFoo.isFoo({})
// ? Uncaught SyntaxError: Private field '#brand' must be declared in an enclosing class#brand in x