是后者,因为当一个Promiseresolved后,它就不能再被rejected。 一旦你调用一种方法(resolve或reject),另一种方法就会失效,因为promise处于稳定状态。让我们探索一个promise的所有不同状态。 1.2 Promise 状态 Promise 可以分为四个状态: ⏳ Pending:初始状态,异步操作仍在进行中。 ✅ Fulfi
ThePromise.allSettled()method is useful when you want to wait for multiple promises to settle, no matter whether they'll be fulfilled or rejected. First thing first, let's understand what is promise state: 'Settled' means both 'Resolved' or 'Rejected'. So in most cases, Promise.settled()...
consta=()=>newPromise((resolve)=>setTimeout(()=>{console.log('a'),resolve()},1e3)); constb=()=>newPromise((resolve)=>setTimeout(()=>{console.log('b'),resolve()},1e3)); constc=()=>newPromise((resolve,reject)=>setTimeout(()=>{console.log('c'),reject('Oops!')},1e3...
我们可以使用Promise.all,它通常在启动多个异步任务并发运行并为其结果创建承诺之后使用,以便人们可以等待所有任务完成。 const axios = require('axios'); const bitcoinPromise = axios.get('https://api.coinpaprika.com/v1/coins/btc-bitcoin/markets'); const dollarPromise = axios.get('https://api.exchange...
Notice that thePromiseobject returned from thePromise.allSettled()method is only rejected if there's an error iterating over the input promises. In all other cases, it is fulfilled. ThePromise.allSettled()method is useful when you want to wait for multiple promises to settle, no matter whether...
then(wait1000) .then(result => { console.log('end', result); }) 在没有Promise之前指定回调函数必须在启动异步任务前进行指定;Promise实现:启动异步任务=>返回Promise对象=>给Promise对象绑定回调函数(甚至可以在异步任务结束后指定多个),大大的增加了我们指定回调函数的灵活性。
then方法接受两个参数,第一个参数是成功时的回调,在promise由“等待”态转换到“完成”态时调用,另一个是失败时的回调,在promise由“等待”态转换到“拒绝”态时调用。同时,then可以接受另一个promise传入,也接受一个“类then”的对象或方法,即thenable对象。
A promise starts in a pending state. That means the process is not complete. If the operation is successful, the process ends in a fulfilled state. And, if an error occurs, the process ends in a rejected state. For example, when you request data from the server by using a promise, it...
n:M))}).promise()},promise:function(e){return null!=e?S.extend(e,a):a}},s={};return S.each(o,function(e,t){var n=t[2],r=t[5];a[t[1]]=n.add,r&&n.add(function(){i=r},o[3-e][2].disable,o[3-e][3].disable,o[0][2].lock,o[0][3].lock),n.add(t[3]....
Convenience utility method to wait for a number of promises to either resolve or reject. The resulting promise resolves to an array of result objects containing the promise and either a value if the promise resolved, or an error if the promise rejected. This is similar to the native Promise....