Preventdefault vs stoppropagation javascript

 Here is a brand new essay about preventDefault() versus stopPropagation() in Angular. I'll start by comparing how they're used with preventDefault() and stopPropagation. We'll also offer a case study for each method and share some tips.

1. event.preventDefault() in Angular

• Purpose: To prevent the default action of a browser event (for example, a submission form or hyperlink).
• Use in Angular: With Angular’s event binding syntax (event)="handler($event)"

.

Example: Prevent link from navigating:

<a href="https://dangerous.com" (click)="onLinkClick($event)">Dangerous Link</a>

onLinkClick(event: MouseEvent) {
  event.preventDefault(); // Stop navigation
  // Custom logic here (e.g., show a modal instead)
}

• Scenarios Commonly Encountered in Angular:
  • When using (submit) and <form> to cancel form submission.
  • Shut off the default behaviors of anchor tags, buttons, or form fields.

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2. event.stopPropagation() in Angular

• Purpose: Stop event bubbling/capturing in the DOM tree.
• Use in Angular: To prevent parent and descendant components from receiving the exact same events.

Example: Don't let a press on a button cause the parent <div> method to fire:

<div (click)="onParentClick()">
  <button (click)="onButtonClick($event)">Click Me</button>
</div>

onButtonClick(event: MouseEvent) {
  event.stopPropagation(); // The mom's onParentClick() will not fire
  // Take care of button click
}

• Specific Cases:
  • Stop nested components from propagating events.
  • Avoid conflict with other handlers dealing in similar space (e.g., dropdown, modals).

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3. Key Differences in Angular

	preventDefault()	stopPropagation()
Focus	Prevent browser from default behavior (e.g., form submit)	Prevent DOM event bubbling/capturing
Use Case in Angular	Cancel navigation, form submission	Parent and child Components surface events in their own spaces
Template Syntax	(submit)="onSubmit($event)"	(click)="onClick($event)"

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4. Using Both Together in Angular

Example: Handle a custom form action without submitting and prevent parent components from interpreting it:

<form (submit)="onFormSubmit($event)">
  <button type="submit">Save</button>
</form>

onFormSubmit(event: Event) {
  event.preventDefault(); // Halt the default form submission
  event.stopPropagation(); // Don't let parent events hear about this
  this.saveData(); // Custom logic here, e.g. http call
}

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5. Angular Special Notes

Event Modifiers

Angular does not provide its own event modifiers like Vue's .prevent or .stop. You need to call the method explicitly instead:

<form (submit)="onSubmit($event)"></form>

onSubmit(event: Event) {
  event.preventDefault(); // Manually call
}

Component Communication

• stopPropagation() only affects DOM events, not Angular's @Output().

Example:

<app-child (customEvent)="onChildEvent()"></app-child>

// ChildComponent
@Output() customEvent = new EventEmitter();
emitEvent() {
  this.customEvent.emit();
  // Whether the parent code listens to DOM event propagation, onChildEvent() will fire
}

Change Detection

• Neither method affects Angular change detection.
• Use NgZone or ChangeDetectorRef when events bypass Angular's domain (for example, setTimeout).

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6. Angular Best Practices

1. How to Break Free from Inline Calls: Place your methods right in the constituent, rather than inside the official template:

   <a href="#" (click)="onClick($event)">Link</a>
   <button (click)="onClick($event)">Link</button>
   

2. For Component Communication, Use EventEmitter : Old-fashioned emit rather than DOM event. Use @Output() Stateless Copy for State Changes: Ensure data is never changed after a call to preventDefault(), to be sure change detection fires.

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7. Common Traps

• Lack of $event: Don’t forget to mention $event in the template:

  <button (click)="onClick">Click</button> ❌ Incorrect
  <button (click)="onClick($event)">Click</button> ✅ Correct
  

• Too Much stopPropagation(): For highly intricate component trees, it can only create debugging headaches.

In Angular:

• preventDefault(): Regulate browser defaults (e.g., forms, links).
• stopPropagation(): Control event flow between some connected DOM elements/components.
• Use both in tandem to finely manage your event firing and your UI experience.