To create a promise that async can return after the setTimeout callback fires, we can wrap the setTimeout function within a promise constructor, as seen in the snippet below:
<br>function setTimeoutReturnPromise(delay) {<br> return new Promise((resolve) => {</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">setTimeout(resolve, delay);});
}
This function takes a delay as an argument and returns a promise. The promise will resolve after the specified delay has elapsed, and the setTimeout function's callback will be executed.
Now, our async function can use the setTimeoutReturnPromise function to create a promise that it can return. This allows us to use the then() method to execute code after the setTimeout callback has been invoked:
<br>async(function() {<br> setTimeoutReturnPromise(5000).then(() => {</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">console.log("async called back");});
});
Since the introduction of ES2015 and modern JavaScript, promises have become built-in features. The syntax has been simplified, as shown below:
<br>function later(delay) {<br> return new Promise((resolve) => {</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">setTimeout(resolve, delay);});
}
Using arrow functions and optional resolution value arguments, the code can be further condensed:
<br>const later = (delay, value) => new Promise(resolve => setTimeout(resolve, delay, value));<br>
If you desire to cancel the timeout, you can return an object with a promise and a cancel method:
<br>const later = (delay, value) => {<br> let timer = 0;<br> let reject = null;<br> const promise = new Promise((resolve, _reject) => {</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">reject = _reject;
timer = setTimeout(resolve, delay, value);});
return {
get promise() { return promise; },
cancel() {
if (timer) {
clearTimeout(timer);
timer = 0;
reject();
reject = null;
}
}};
};
This approach allows you to cancel the timeout and reject the promise using the cancel() method.
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