fix(promisify): listeners not always removed

Event listeners in `hasFired` are registered with the `once` flag.
This only ensures that either the success OR the error listener is
removed though.

Author: gruhn

src/misc/camera.js

@@ -23,7 +23,7 @@ export default async function(constraints, videoEl) {
   }
 
   const stream = await navigator.mediaDevices.getUserMedia(constraints);
-  const streamLoaded = hasFired(videoEl, "loadeddata", "error");
+  const streamLoaded = hasFired(videoEl, "loadeddata");
 
   if (videoEl.srcObject !== undefined) {
     videoEl.srcObject = stream;

src/misc/promisify.js

@@ -1,9 +1,18 @@
-export function hasFired(element, successEvent, errorEvent) {
-  return new Promise((resolve, reject) => {
-    element.addEventListener(successEvent, resolve, { once: true });
+export function hasFired(eventTarget, successEvent, errorEvent = "error") {
+  let $resolve, $reject;
 
-    if (errorEvent !== undefined) {
-      element.addEventListener(errorEvent, reject, { once: true });
-    }
+  const promise = new Promise((resolve, reject) => {
+    $resolve = resolve;
+    $reject = reject;
   });
+
+  eventTarget.addEventListener(successEvent, $resolve);
+  eventTarget.addEventListener(errorEvent, $reject);
+
+  promise.finally(() => {
+    eventTarget.removeEventListener(successEvent, $resolve);
+    eventTarget.removeEventListener(errorEvent, $reject);
+  });
+
+  return promise;
 }

src/misc/scanner.js

@@ -1,18 +1,17 @@
 import "webrtc-adapter";
+import { hasFired } from "./promisify.js";
 import Worker from "./worker.js";
 
-export function scan(imageData) {
+export async function scan(imageData) {
   const worker = new Worker();
 
-  return new Promise(resolve => {
-    worker.onmessage = event => {
-      resolve(event.data);
+  worker.postMessage(imageData, [imageData.data.buffer]);
 
-      worker.terminate();
-    };
+  const event = await hasFired(worker, "message");
+
+  worker.terminate();
 
-    worker.postMessage(imageData, [imageData.data.buffer]);
-  });
+  return event.data;
 }
 
 /**