I have been trying to perform a test for angular 2 application that clicks a submit button which calls a function. I usually use two methods to perform the same.
element.nativeElement.click()
and
element.triggerEventHandler('click',null);
I thought both these methods were same, until I came across this situation where triggering event handler method does not work.
element = fixture.debugElement.query(By.css('.dropList li'));
element.triggerEventHandler('click',null); //Click event works here
fixture.detectChanges();
let button = fixture.debugElement.query(By.css('button'));
//button.triggerEventHandler('click',null); //Does not call function
button.nativeElement.click(); //Calls function
fixture.detectChanges();
Template for your reference:
<form (ngSubmit)="printSelection()">
<div class="dropList">
<ul>
<li *ngFor="let element of data.elements" (click)="selectElement(element)"> </li>
</ul>
</div>
<button type="submit">Submit</button>
</form>
So, are there any difference between these two approaches or do you think I may have gone wrong somewhere in my code?
element.nativeElement.click()
is native method to simulate a mouse click on an element. It's bubbling and it behaves in the same way as if we click on the element.
debugElement.triggerEventHandler(eventName, eventObj)
is angular built-in method that just calls all listeners for given eventName on current debug element:
triggerEventHandler(eventName: string, eventObj: any) {
this.listeners.forEach((listener) => {
if (listener.name == eventName) {
listener.callback(eventObj);
}
});
}
Listeners are added when DebugRenderer2 runs listen method:
listen(
target: 'document'|'windows'|'body'|any, eventName: string,
callback: (event: any) => boolean): () => void {
if (typeof target !== 'string') {
const debugEl = getDebugNode(target);
if (debugEl) {
debugEl.listeners.push(new EventListener(eventName, callback));
}
}
return this.delegate.listen(target, eventName, callback);
}
It happens when we apply event binding to element like
(click)="handler()" @HostListener('click') host: '{ '(mouseenter): 'handler()' } renderer.listen
Let's say we have the following template:
<div (click)="test()">
<div class="innerDiv">
{{title}}
</div>
</div>
And our test will look like:
de = fixture.debugElement.query(By.css('.innerDiv'));
de.nativeElement.click(); // event will be bubbled and test handler will be called
de.triggerEventHandler('click', null); // there is not handlers for click event
// that angular added to this element
// so test method won't be called
Then let's look at your template. There is no handlers for button so triggerEventHandler won't have any effect. On the other hand button.nativeElement.click(); will fire submit because button has type submit and its standart behaviour of button on click event.
