Add aborted property to API responses

This makes it easy to test whether an API request failed because it was aborted.

h/static/scripts/group-forms/utils/api.ts

@@ -87,6 +87,14 @@ export class APIError extends Error {
     this.response = response;
     this.json = json;
   }
+
+  /**
+   * Property that is true if the API call failed because the operation was
+   * aborted.
+   */
+  get aborted() {
+    return this.cause?.name === 'AbortError';
+  }
 }
 
 export type APIOptions = {

h/static/scripts/group-forms/utils/test/api-test.js

@@ -9,7 +9,7 @@ describe('callAPI', () => {
   });
 
   afterEach(() => {
-    window.fetch.restore();
+    window.fetch.restore?.();
   });
 
   context('when the API responds successfully', () => {
@@ -138,6 +138,23 @@ describe('callAPI', () => {
     assert.calledWith(fakeFetch, paginatedURL.toString());
   });
 
+  it('rejects with aborted APIError if request is aborted', async () => {
+    window.fetch.restore();
+
+    const ac = new AbortController();
+    ac.abort();
+
+    let error;
+    try {
+      await callAPI(url, { signal: ac.signal });
+    } catch (e) {
+      error = e;
+    }
+
+    assert.instanceOf(error, APIError);
+    assert.isTrue(error.aborted);
+  });
+
   [
     {
       response: new Response(