Function scheduleTask

packages/zone.js/lib/browser/browser.ts:133–195

(task: Task)

      const SCHEDULED = 'scheduled';

      function scheduleTask(task: Task) {
        const data = <XHROptions>task.data;
        const target = data.target;
        target[XHR_SCHEDULED] = false;
        target[XHR_ERROR_BEFORE_SCHEDULED] = false;
        // remove existing event listener
        const listener = target[XHR_LISTENER];
        if (!oriAddListener) {
          oriAddListener = target[ZONE_SYMBOL_ADD_EVENT_LISTENER];
          oriRemoveListener = target[ZONE_SYMBOL_REMOVE_EVENT_LISTENER];
        }

        if (listener) {
          oriRemoveListener.call(target, READY_STATE_CHANGE, listener);
        }
        const newListener = (target[XHR_LISTENER] = () => {
          if (target.readyState === target.DONE) {
            // sometimes on some browsers XMLHttpRequest will fire onreadystatechange with
            // readyState=4 multiple times, so we need to check task state here
            if (!data.aborted && target[XHR_SCHEDULED] && task.state === SCHEDULED) {
              // 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 (target.status !== 0 && loadTasks && loadTasks.length > 0) {
                const oriInvoke = task.invoke;
                task.invoke = function () {
                  // need to load the tasks again, because in other
                  // load listener, they may remove themselves
                  const loadTasks = target[Zone.__symbol__('loadfalse')];
                  for (let i = 0; i < loadTasks.length; i++) {
                    if (loadTasks[i] === task) {
                      loadTasks.splice(i, 1);
                    }
                  }
                  if (!data.aborted && task.state === SCHEDULED) {
                    oriInvoke.call(task);
                  }
                };
                loadTasks.push(task);
              } else {
                task.invoke();
              }
            } else if (!data.aborted && target[XHR_SCHEDULED] === false) {
              // error occurs when xhr.send()
              target[XHR_ERROR_BEFORE_SCHEDULED] = true;
            }
          }
        });
        oriAddListener.call(target, READY_STATE_CHANGE, newListener);

        const storedTask: Task = target[XHR_TASK];
        if (!storedTask) {
          target[XHR_TASK] = task;