您可以在 4 中使用的顶级 Javascript 功能

const user = { profile: { bio: { name: 'jane doe' } } };console.log(user?.profile?.bio?.name); // outputs: jane doe

const userinput = null;const username = userinput ?? 'guest';console.log(username); // outputs: guest

const bignumber = 9007199254740991n + 1n;console.log(bignumber); // outputs: 9007199254740992n

if (condition) {  import('./module.js').then((module) => {    module.default();  });}

const promises = [fetch('/api'), fetch('/other-api')];promise.allsettled(promises).then((results) =>  results.foreach((result) => console.log(result.status)));

class myclass {  #privatefield = 42;  getprivatefield() {    return this.#privatefield;  }}const myinstance = new myclass();console.log(myinstance.getprivatefield()); // outputs: 42

let a = 0;a ||= 1; // a becomes 1 if it's falsyconsole.log(a); // outputs: 1

const text = 'hello world! hello universe!';const newtext = text.replaceall('hello', 'hi');console.log(newtext); // outputs: hi world! hi universe!

let obj = { data: 'important' };const weakref = new weakref(obj);obj = null; // obj can now be garbage-collected

const data = await fetch('/api').then((res) => res.json());console.log(data);