正儿八经 - 资深软件工程师

const foo = null ?? 'default string';
console.log(foo);
// expected output: "default string"

const baz = 0 ?? 42;
console.log(baz);
// expected output: 0

if( a && a.b  && a.b.c){
    //do something...
}
//可换成：
if( a?.b?c){
    //do something...
}


const a={}
const test=a?.b?.c
// expected output: undefined

Promise.race([
  new Promise((resolve, reject) => setTimeout(reject, 200, 'Third')),
  new Promise((resolve, reject) => setTimeout(resolve, 1000, 'Second')),
  new Promise((resolve, reject) => setTimeout(resolve, 2000, 'First')),
])
.then(value => console.log(`Result: ${value}`))
.catch (err => console.log(err))
// expected output: Third


Promise.any([
  new Promise((resolve, reject) => setTimeout(reject, 200, 'Third')),
  new Promise((resolve, reject) => setTimeout(resolve, 1000, 'Second')),
  new Promise((resolve, reject) => setTimeout(resolve, 2000, 'First')),
])
.then(value => console.log(`Result: ${value}`))
.catch (err => console.log(err))
// expected output: Second

const str = "zhangsan is wangmazi's 舅子,wangmazi is zhangsan's 妹夫";
const newStr = str.replace("is", "isn't");
console.log(newStr); 
// expected output:zhangsan isn't wangmazi's 舅子,wangmazi is zhangsan's 妹夫

// 替换所有,只能用正则
const newStr = str.replace(/is/g, "isn't");
console.log(newStr);
//expected output: zhangsan isn't wangmazi's 舅子,wangmazi isn't zhangsan's 妹夫

const str = "zhangsan is wangmazi's 舅子,wangmazi is zhangsan's 妹夫";
const newStr = str.replaceAll("is", "isn't");
console.log(newStr); 
// expected output: zhangsan isn't wangmazi's 舅子,wangmazi isn't zhangsan's 妹夫

x ||= y;
// 等同
x || (x = y);
 
x &&= y;
// 等同
x && (x = y); 
// 或者
if(x) {
  x = y
}
 
x ??= y;
// 等同
x ?? (x = y);


// 比如
let x = 1;
let y = 2;
x &&= y;
console.log(x); 
//expected output: 2
 

const billion = 1000_000_000;
console.log(billion); 
//expected output:1000000000
const trillion = 1000_000_000_000n;
console.log(trillion.toString()); 
//expected output: "1000000000000"
console.log(1000_000_000 === 1000000000); 
//expected output: true

const p1 = new Promise((resolve, reject) => setTimeout(resolve, 1000,'failed'));
const p2 = new Promise((resolve, reject) => setTimeout(reject, 2000,'a'));
const p3 = new Promise((resolve, reject) => setTimeout(resolve, 3000,'b'));
// 返回值对象：fulfilled时，对象有value属性，rejected时有reason属性
Promise.allSettled([p1, p2, p3]).then(values => console.log(values));

//expected output: Array
// 0: {status: "fulfilled", value: "failed"}
// 1: {status: "rejected", reason: "a"}
// 2: {status: "fulfilled", value: "b"}