中止ecmascript7异步功能 [英] Abort ecmascript7 async function
问题描述
是否可以取消ES7异步功能?
Is there a way to cancel a ES7 async function?
在此示例中,单击时,我想在调用new之前中止异步功能调用。
In this example, on click, I want to abort async function call before calling new.
async function draw(){
for(;;){
drawRandomRectOnCanvas();
await sleep(100);
}
}
function sleep(t){
return new Promise(cb=>setTimeout(cb,t));
}
let asyncCall;
window.addEventListener('click', function(){
if(asyncCall)
asyncCall.abort(); // this dont works
clearCanvas();
asyncCall = draw();
});
推荐答案
JavaScript尚未内置任何功能,但是您可以
There's nothing built in to JavaScript yet, but you could easily roll your own.
MS.Net使用取消令牌的概念来取消任务(相当于Promises的.net)。效果很好,因此这是JavaScript的简化版本。
MS.Net uses the concept of a cancellation token for the cancelling of Tasks (the .net equivalent of Promises). It works quite nicely, so here's a cut-down version for JavaScript.
假设您制作了一个旨在表示取消的类:
Say you made a class that is designed to represent cancellation:
function CancellationToken(parentToken){
if(!(this instanceof CancellationToken)){
return new CancellationToken(parentToken)
}
this.isCancellationRequested = false;
var cancellationPromise = new Promise(resolve => {
this.cancel = e => {
this.isCancellationReqested = true;
if(e){
resolve(e);
}
else
{
var err = new Error("cancelled");
err.cancelled = true;
resolve(err);
}
};
});
this.register = (callback) => {
cancellationPromise.then(callback);
}
this.createDependentToken = () => new CancellationToken(this);
if(parentToken && parentToken instanceof CancellationToken){
parentToken.register(this.cancel);
}
}
然后您更新了睡眠功能以了解此信息令牌:
then you updated your sleep function to be aware of this token:
function delayAsync(timeMs, cancellationToken){
return new Promise((resolve, reject) => {
setTimeout(resolve, timeMs);
if(cancellationToken)
{
cancellationToken.register(reject);
}
});
}
现在您可以使用令牌取消传递给它的异步功能:
Now you can use the token to cancel the async function that it was passed to:
var ct = new CancellationToken();
delayAsync(1000)
.then(ct.cancel);
delayAsync(2000, ct)
.then(() => console.log("ok"))
.catch(e => console.log(e.cancelled ? "cancelled" : "some other err"));
http://codepen.io/spender/pen/vNxEBZ
...或使用async /或多或少地做同一件事而是等待方式:
...or do more or less the same thing using async/await style instead:
async function Go(cancellationToken)
{
try{
await delayAsync(2000, cancellationToken)
console.log("ok")
}catch(e){
console.log(e.cancelled ? "cancelled" : "some other err")
}
}
var ct = new CancellationToken();
delayAsync(1000).then(ct.cancel);
Go(ct)
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