"chrome: invoking 'alert()' during microtask execution is deprecated and will be removed" Code Answer

yes, the warning is justified: you're calling alert within a microtask, in this case a promise completion. (see difference between microtask and macrotask within an event loop context.)

alert, prompt, and confirm are relics of an age long past, and they have a problem: they completely interrupt the normal workings of javascript and arguably violate its run-to-completion semantics by completely suspending execution, right in the middle of a job from the job queue (or a task from the event loop; javascript and the html5 spec differ on terminology) and do ui in the form of a blocking modal. this is just not in keeping with the general mode of interaction, which is event-based (show the message, get an event when it's closed).

you can work around it by doing the alert in a macrotask instead:

this.service.uploadfile((error: any) => {
    if (error) {
        settimeout(() => {
            console.log(error);
            alert("an error occured");
        }, 0);
        return;
    }

    this.onuploadcompleted()
});

...but really the solution is to stop using alert, prompt, and confirm entirely.

here's a fun example of micro and macro tasks: a promise completion is a microtask, whereas timer callbacks are macrotasks. the initial run of the script is also a macrotask, as is a dom event callback. all of the microtasks queued by a macrotask are run before the next macrotask is run; e.g., they jump the queue. so with this:

// first, we set a timer callback for 0ms
settimeout(() => {
  console.log("timer fired");
}, 0);

// now we get a promise that's *already* resolved and hook a callback
promise.resolve().then(() => {
  console.log("promise resolved");
});

// now show a message demonstrating we got here before the promise resolution callback
console.log("got to the end");

...we see

got to the end
promise resolved
timer fired

...rather than

got to the end
timer fired
promise resolved

....which we would have gotten if all tasks were created equal.