Angular 2: Debounce (ngModelChange)?

Question

Is there a way to debounce the template directive (ngModelChange) ?

Or, alternatively, what is the least-painful way to do it a different way?

The closest answer I see is this: How to watch for form changes in Angular 2?

So, for example, I have a text input, I want to get onChange updates, but I want to debounce it down from every keystroke:

<input type="text" class="form-control" placeholder="Enter a value" name="foo" [(ngModel)]="input.event.value" (ngModelChange)="onFieldChange($event, input)">

Debounce onFieldChange()

Answer 1

EDIT

In new version of Angular you can use updateOn in ngModelOption to set 'blur' for example. Link to angular.io documentation .

Code example :

<input [(ngModel)]="value"
  [ngModelOptions]="{ updateOn: 'blur' }"
  (ngModelChange)="updateOnlyOnBlur($event)"> 

LEGACY

Here's the less painful way of debouncing keystrokes if you don't want to use the formcontrol approach.

search.component.html

<input type="text" placeholder="Enter a value" name="foo" [(ngModel)]="txtQuery" (ngModelChange)="onFieldChange($event)">

search.component.ts

    export class SearchComponent {
    
         txtQuery: string; // bind this to input with ngModel
         txtQueryChanged: Subject<string> = new Subject<string>();
    
         constructor() {
          this.txtQueryChanged
            .debounceTime(1000) // wait 1 sec after the last event before emitting last event
            .distinctUntilChanged() // only emit if value is different from previous value
            .subscribe(model => {
              this.txtQuery = model;
    
              // Call your function which calls API or do anything you would like do after a lag of 1 sec
              this.getDataFromAPI(this.txtQuery);
             });
        }
    
    onFieldChange(query:string){
      this.txtQueryChanged.next(query);
    }
}

Answer 2

For RxJs 6+

The chosen answer won't work for RxJs 6+. Here is what you have to change:

The imports have to look like this:

import {Subject} from "rxjs";
import {debounceTime, distinctUntilChanged} from "rxjs/operators";

You need to call pipe :

// ...
this.txtQueryChanged
   .pipe(debounceTime(1000), distinctUntilChanged())
   .subscribe(model => {
       this.txtQuery = model;
       // api call
   });
 // ...

Take a look atthis article for further reading.

Answer 3

I've written a little directive to solve this.

How to use it:

<input [ngModel]="someValue" (ngModelChangeDebounced)="someValue = $event">

You can optionally set a debounce time (default is 500):

[ngModelChangeDebounceTime]="200"

The directive itself:

@Directive({
  selector: '[ngModelChangeDebounced]',
})
export class NgModelChangeDebouncedDirective implements OnDestroy {
  @Output()
  ngModelChangeDebounced = new EventEmitter<any>();
  @Input()
  ngModelChangeDebounceTime = 500; // optional, 500 default

  subscription: Subscription;
  ngOnDestroy() {
    this.subscription.unsubscribe();
  }

  constructor(private ngModel: NgModel) {
    this.subscription = this.ngModel.control.valueChanges.pipe(
      skip(1), // skip initial value
      distinctUntilChanged(),
      debounceTime(this.ngModelChangeDebounceTime)
    ).subscribe((value) => this.ngModelChangeDebounced.emit(value));
  }
}

Stackblitz: https://stackblitz.com/edit/angular-9-0-0-rc-1-y2q2ss

Answer 4

If you wanted to add debounceTime while doing http call you can use Subject which is very easy to use . Which is also explained in angular2 tutorial - HTTP .