延迟后的承诺

Question

我有这个问题，我似乎不知道如何解决？写一个函数，承诺，接受一个值。此函数将返回一个承诺，该承诺将在 2 秒后解决。下面的代码不应该被编辑并且应该使用 promise 对象。

 function promised (val) {

     

    }

    

    // UNCOMMENT THESE TO TEST YOUR WORK!

     const createPromise = promised('wait for it...');

     createPromise.then((val) => console.log(val)); 

    // will log "wait for it..." to the console after 2 seconds

Answer 1

const sleep = async (time) => {    return new Promise(resolve => setTimeout(resolve, time * 1000))}const sayHello = async () => {    await sleep(2)    console.log('Hello there')}sayHello()这是解释：使用setTimeout()which 是一种内置方法，可在指定的毫秒数后调用函数或计算表达式。 setTimeout()有两个参数，第一个是回调函数，第二个是毫秒数。1 秒 = 1000 毫秒所以 2 秒 = 2000 毫秒等等function promised (val) {    // Create a new promise and resolve val after 2 seconds    return new Promise(resolve => setTimeout(() => resolve(val), 2000)) //2000ms => 2 seconds}const createPromise = promised('wait for it...') // Pass in your message to promised functioncreatePromise    .then(val => console.log(val))    // Catch errors if any you don't need it here since we are always resolving the promise i just included it here so you know it's exist     .catch(err => console.log(err)) 你应该总是使用 .catch 除非你 100% 确定承诺总是会解决例子：function greeting(name) {    return new Promise((resolve, reject) => setTimeout(() => {                try {                        if (name.length <= 2) {                throw new Error('Name must be more than two characters')            }        } catch (msg) {            reject(msg)        }         resolve(`Hello ${name}`)                    }, 2000))}greeting('ab')    .then(res => console.log(res))    .catch(err => console.log(err)) // Error: Name must be more than two charactersgreeting('John')    .then(res => console.log(res)) // Hello John    .catch(err => console.log(err))使用异步，等待：const greetSomeone = async (name) => {    try {        // Note that you can't use await outside an async function        const msg = await greeting(name)         console.log(msg)    } catch (err) {        console.log(err)    }}greetSomeone('ac') // Error: Name must be more than two charactersgreetSomeone('Michael') // Hello Michael