I am currently delving into the world of Angular 2.0 and stumbled upon the mysterious file known as Zone.js. I am curious to understand the role of Zone.js and how it can enhance the performance of my application.
I am currently delving into the world of Angular 2.0 and stumbled upon the mysterious file known as Zone.js. I am curious to understand the role of Zone.js and how it can enhance the performance of my application.
A zone is a specific context in which asynchronous tasks persist, allowing the creator to monitor and manage the code execution within that zone.
One of the primary reasons for utilizing zone.js in Angular 2 is to determine the optimal time for rendering.
Referencing the NgZone Primer (Chapter 5: Use Cases/Use Case 3: Framework Auto Render), frameworks like Angular require insight into when all application tasks are finished to update the DOM before pixel rendering by the host environment. This entails the framework being aware when the main task and associated micro tasks have been completed, just before the VM relinquishes control to the host.
Angular leverages the zone to modify async APIs (such as addEventListener, setTimeout(), ...) and utilizes notifications from these modified APIs to run change detection whenever an async event occurs.
The Angular zone includes an onMicrotaskEmpty event.
https://github.com/angular/angular/blob/2.2.4/modules/%40angular/core/src/zone/ng_zone.ts#L199
The ApplicationRef subscribes to this event to initiate change detection (Application.tick).
Furthermore, zone.js proves beneficial for debugging, testing, and profiling, aiding in seeing the complete call stack when encountering errors.
Zone patches various async APIs, including:
Promise
XHR
fetch
Error
... (full list of patched APIs)
These articles offer valuable insights into understanding how zone.js operates within Angular 2:
Zone.js plays a vital role in Angular's change detection mechanism.
By encapsulating all asynchronous tasks in the browser like user interactions, HTTP requests, timers, and other state-altering operations, Zone keeps track of when these tasks are completed. Angular, on the other hand, relies on notifications from Zone to trigger its change detection process after each operation completion. This ensures that Angular updates only what has changed, reducing unnecessary rendering processes and optimizing performance.
Zonejs plays a crucial role as a core library in Angularjs 2, serving to maintain contextual execution for both single and multi-leveled asynchronous methods. Essentially, it aids in tracking the parent context of the currently executing asynchronous methods.
For instance -
Zone.current.fork({}).run(function(){
Zone.current.myZoneVar = true;
console.log('Assigned myZoneVar');
setTimeout(()=>{
console.log('In timeout', Zone.current.myZoneVar);
},1000);
});
console.log('Out side', Zone.current.myZoneVar);<script src="https://unpkg.com/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="2e5441404b00445d6e1e0016001a">[email protected]</a>?main=browser"></script>Note : Please disregard any console errors. This code functions correctly in jsfiddle - https://jsfiddle.net/subhadipghosh/0uqc9rdr/
In the above example, we have created a new Zone by forking our current Zone and then running a method within it. This method includes an asynchronous call (setTimeout). Since the method is within the Zone, we have access to the Zone variable. However, when attempting to access the same variable outside of the Zone in the last line, it will return undefined.
Original source -
Zonejs is extensively utilized by Angular 2 for change detection. The following code snippet in Angular 2 is responsible for detecting any changes that occur:
ObservableWrapper.subscribe(this.zone.onTurnDone, () => {
this.zone.run(() => {
this.tick();
});
});
tick() {
// perform change detection
this.changeDetectorRefs.forEach((detector) => {
detector.detectChanges();
});
}
The Angular zone emits the onTurnDone event to initiate change detection within the application.
Put simply, Zone.js is an API or collection of programs utilized by Angular 2 to refresh the application view whenever a change occurs.
A Zone is a runtime environment that remains consistent throughout asynchronous tasks, such as events, XMLHttpRequests, and timers (e.g. setTimeout(), setInterval()).
Zone.js is utilized for asynchronous calls and is also used internally by Angular 2 for error handling and generating stack traces. It is an essential script that cannot be overlooked.
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