fix(zone.js): should invoke xhr send task when no response error occu…

…rs (angular#38836)

Close angular#38795

in the XMLHttpRequest patch, when get `readystatechange` event, zone.js try to
invoke `load` event listener first, then call `invokeTask` to finish the
`XMLHttpRequest::send` macroTask, but if the request failed because the
server can not be reached, the `load` event listener will not be invoked,
so the `invokeTask` of the `XMLHttpRequest::send` will not be triggered either,
so we will have a non finished macroTask there which will make the Zone
not stable, also memory leak.

So in this PR, if the `XMLHttpRequest.status = 0` when we get the `readystatechange`
event, that means something wents wrong before we reached the server, we need to
invoke the task to finish the macroTask.

PR Close angular#38836

packages/zone.js/lib/browser/browser.ts

@@ -149,8 +149,12 @@ Zone.__load_patch('XHR', (global: any, Zone: ZoneType) => {
             // check whether the xhr has registered onload listener
             // if that is the case, the task should invoke after all
             // onload listeners finish.
+            // Also if the request failed without response (status = 0), the load event handler
+            // will not be triggered, in that case, we should also invoke the placeholder callback
+            // to close the XMLHttpRequest::send macroTask.
+            // https://github.com/angular/angular/issues/38795
             const loadTasks = target[Zone.__symbol__('loadfalse')];
-            if (loadTasks && loadTasks.length > 0) {
+            if (target.status !== 0 && loadTasks && loadTasks.length > 0) {
               const oriInvoke = task.invoke;
               task.invoke = function() {
                 // need to load the tasks again, because in other

packages/zone.js/test/browser/XMLHttpRequest.spec.ts

@@ -268,6 +268,30 @@ describe('XMLHttpRequest', function() {
        });
      });
 
+  it('should close xhr request if error happened when connect', function(done) {
+    const logs: boolean[] = [];
+    Zone.current
+        .fork({
+          name: 'xhr',
+          onHasTask:
+              (delegate: ZoneDelegate, curr: Zone, target: Zone, taskState: HasTaskState) => {
+                if (taskState.change === 'macroTask') {
+                  logs.push(taskState.macroTask);
+                }
+                return delegate.hasTask(target, taskState);
+              }
+        })
+        .run(function() {
+          const req = new XMLHttpRequest();
+          req.open('get', 'http://notexists.url', true);
+          req.send();
+          req.addEventListener('error', () => {
+            expect(logs).toEqual([true, false]);
+            done();
+          });
+        });
+  });
+
   it('should trigger readystatechange if xhr request trigger cors error', (done) => {
     const req = new XMLHttpRequest();
     let err: any = null;