Add AbortController related helpers

These allow linking multiple AbortControllers and ceate a timeout abort signal.

For example in case you want to abort a fetch in case

(1) the UI element gets removed
(2) a newer request replacing this one gets started
(3) a timeout happens because the fetch takes too long

createLinkedAbortController() allows merging multiple signals into one
and createTimeoutAbortSignal() allows creating a singal that auto aborts
after some time passes.

packages/common/index.js

-import {EventBus} from './eventbus.js';
+import {EventBus} from './src/eventbus.js';
+import {createLinkedAbortController, createTimeoutAbortSignal} from './src/abort.js';
 
-export {EventBus};
\ No newline at end of file
+export {EventBus, createLinkedAbortController, createTimeoutAbortSignal};
\ No newline at end of file

packages/common/src/abort.js

+/**
+ * Takes multiple AbortSignal instances and returns a new AbortController which
+ * gets aborted if any of the AbortSignals do.
+ *
+ * @param  {...AbortSignal} signals
+ * @returns {AbortController}
+ */
+export function createLinkedAbortController(...signals) {
+    const controller = new AbortController();
+
+    for (const signal of signals) {
+        if (signal.aborted) {
+            controller.abort();
+            break;
+        } else {
+            signal.addEventListener('abort', () => {
+                controller.abort();
+            });
+        }
+    }
+
+    return controller;
+}
+
+/**
+ * Returns an AbortSignal which aborts after the specified time.
+ *
+ * @param {number} delay Delay in milliseconds
+ * @returns {AbortSignal}
+ */
+export function createTimeoutAbortSignal(delay) {
+    const controller = new AbortController();
+
+    setTimeout(() => {controller.abort(); }, delay);
+
+    return controller.signal;
+}
\ No newline at end of file

packages/common/test/abort.js

+import {assert} from 'chai';
+import {createLinkedAbortController, createTimeoutAbortSignal} from '../src/abort.js';
+
+suite('abort', () => {
+    test('createLinkedAbortController', () => {
+        let c1 = new AbortController();
+        let c2 = new AbortController();
+        const linked = createLinkedAbortController(c1.signal, c2.signal);
+        assert.isFalse(linked.signal.aborted);
+        c1.abort();
+        assert.isTrue(linked.signal.aborted);
+        c1.abort();
+        linked.abort();
+    });
+
+    test('createTimeoutAbortSignal', () => {
+        const signal = createTimeoutAbortSignal(10000000);
+        assert.isFalse(signal.aborted);
+    });
+});
\ No newline at end of file

packages/common/test/eventbus.js

 import {assert} from 'chai';
-import {EventBus, createEventName, checkIndentifier} from '../eventbus.js';
+import {EventBus, createEventName, checkIndentifier} from '../src/eventbus.js';
 
 suite('helpers', () => {
     test('createEventName', () => {