如果handler返回一个settled的Promise对象temp,p2状态立即(synchronously)变化:pending-->与temp相同的状态,且p2的[[PromiseValue]]与temp的[[PromiseValue]]相同。 如果handler返回一个pending的Promise对象temp,p2的状态不立即改变,而是等到temp进入settled状态以后,p2的状态再(异步地)改变:pending-->与temp相同的状态,...
constp =Promise.all([]);// synchronously, will be immediately resolvedconstp2 =Promise.all([1337,"hi"]);// non-promise values will be ignored, but the evaluation will be done asynchronouslyconsole.log(p);console.log(p2)setTimeout(function() {console.log('the stack is now empty');conso...
promise['_resolves'] = promise['_rejects'] =undefined; }varPromise =function(resolver){if(!isFunction(resolver))thrownewTypeError('You must pass a resolver function as the first argument to the promise constructor');if(!(thisinstanceofPromise))returnnewPromise(resolver);varpromise =this; promis...
We can create a promise (small p) using new Promise (capital P).const promise = new Promise(executorCallback); CopyPromises are so-called because when we place a Promise in our code, we are promising we’ll get the result of an asynchronous operation back at some point. The result ...
async/await and promise/promise.all used in combination to achieve flexible part of the task concurrent execution, part of the task synchronously. async function batchExec() { console.group("batchExec") let startTime = new Date().getTime() console.log("batchExec start", startTime) // 等待...
Iterable Promise Observable AsyncIterable Getter-getter Setter-setter Getter Setter Function Value Iterables can represent any infinite or finite sequence of values, but they have one limitation: the value must be synchronously available as soon as the consumer calls the next() method. AsyncIterable...
They are a little slower than callbacks, but in return we get a lot of trustability. We can always be sure that a Promise will resolve or reject since they are a “wrapper” around a value that may not exist yet. Promises are a trustable mechanism that also helps to express async...
This kind-of result object that encapsulates (aka holds, manages, contains) the result of an asynchronous operation is a promise object.Promises, wrapping the asynchronous operation result, can be returned synchronously from a function, assigned to variables, or used as arguments. That's the idea...
getJSON()发起一个 HTTP 请求然后返回 Promise 对象,这个对象定义了一个then()实例方法。上面的是直接把回调函数传入 getText() 方法,这里我们则是把它传到then()方法里。 你可以把then()方法想象成回调函数注册处理中心,就像addEventListener()方法。如果你多次调用 then() 方法,那么每个都会在上一个异步计算结束完...
The following is the service worker code to reproduce the problem: self.addEventListener('fetch', (event) => { if (event.request.url.includes('test.html')) { event.respondWith(longRunFetch()); } }); async function longRunFetch(request) { await new Promise(resolve => setTimeout(resolve...