How to check if a Promise is pending
Solution 1
You can attach a then
handler that sets a done
flag on the promise (or the RunTest
instance if you prefer), and test that:
if (!this.promise) {
this.promise = this.someTest();
this.promise.catch(() => {}).then(() => { this.promise.done = true; });
retVal = true;
}
if ( this.promise.done ) {
this.promise = this.someTest();
this.promise.catch(() => {}).then(() => { this.promise.done = true; });
retVal = true;
}
Notice the empty catch()
handler, it's crucial in order to have the handler called regardless of the outcome of the promise.
You probably want to wrap that in a function though to keep the code DRY.
Solution 2
class RunTest {
constructor() {
this.isRunning = false;
}
start() {
console.log('isrunning', this.isRunning);
var retVal = false;
if(!this.isRunning) {
this.promise = this.someTest();
this.promise.catch().then(() => { this.isRunning = false; });
retVal = true;
}
return retVal;
}
someTest() {
this.isRunning = true;
return new Promise((resolve, reject) => {
setTimeout(function() {
//some tests go inhere
resolve();
}, 1000);
});
}
};
var x = new RunTest();
x.start(); //logs false
x.start(); //logs true
setTimeout(function() {
//wait for a bit
x.start(); //logs false
}, 2000);
Jeanluca Scaljeri
Updated on July 09, 2022Comments
-
Jeanluca Scaljeri almost 2 years
I have this situation in which I would like to know what the status is of a promise. Below, the function
start
only callssomeTest
if it is not running anymore (Promise is not pending). Thestart
function can be called many times, but if its called while the tests are still running, its not going to wait and returns justfalse
class RunTest { start() { retVal = false; if (!this.promise) { this.promise = this.someTest(); retVal = true; } if ( /* if promise is resolved/rejected or not pending */ ) { this.promise = this.someTest(); retVal = true; } return retVal; } someTest() { return new Promise((resolve, reject) => { // some tests go inhere }); } }
I cannot find a way to simply check the status of a promise. Something like
this.promise.isPending
would be nice :) Any help would be appreciated!