“Trim” directive for angular 2 and reflect changes to ngModel

Question

I want to create Angular 2 directive that will tirm spaces only from begining and the end of the text that user has typed into input field.

I have input field

<input trim name="fruit" [(ngModel)]="fruit"/>

and directive

import {Directive, ElementRef} from "@angular/core";

@Directive({
  selector: 'input[trim]',
  host: {'(blur)': 'onChange($event)'}
})

export class TrimWhiteSpace {

  constructor(private cdRef:ChangeDetectorRef, private el: ElementRef){}

  onChange($event:any) {
    let theEvent = $event || window.event;
    theEvent.target.value = theEvent.target.value.trim();
  }
}

which works fine, removes spaces and changes text in input field, but the problem is that the value in ngModel variable "fruit" is not changed and it still contains text with spaces at the begining or at the end.

I also tried to add following to onChange method

this.el.nativeElement.value = theEvent.trim();
this.cdRef.detectChanges();

and change form (blur) to (ngModelChange), but text in ngModel is not effected.

Any suggestions?

Answer 1

Have you looked at https://github.com/anein/angular2-trim-directive ?

Seems like it would address your use case

Answer 2

to avoid confusion changing model attribute name.

<input name="fruit" [(ngModel)]="fruit1" (change)="fruit1=fruit1.trim()"/>

Answer 3

CommonController in example is just base class that triggers subject in onDestroy hook to unsubsribe from observable.

@Directive({
  selector: '[appTrimOnBlur]'
})
export class TrimOnBlurDirective extends CommonController implements OnInit {

  constructor(private elementRef: ElementRef,
              @Self() private ngControl: NgControl) {
    super();
  }

  ngOnInit(): void {
    fromEvent(this.elementRef.nativeElement, 'blur').pipe(
      takeUntil(this.unsubscribeOnDestroy)
    ).subscribe(() => {
      const currentValue: string = this.ngControl.value.toString();
      const whitespace: string = ' ';
      if (currentValue.startsWith(whitespace) || currentValue.endsWith(whitespace)) {
        this.ngControl.control.patchValue(currentValue.trim());
      }
    });
  }

}

You can create generic trim directive, that will make trim not only for blur event,but for any, that you will provide:

@Input() public trimEventName: string = 'blur';

  constructor(private elementRef: ElementRef,
              @Self() private ngControl: NgControl) {
    super();
  }

  ngOnInit(): void {
    fromEvent(this.elementRef.nativeElement, this.trimEventName).pipe(
      takeUntil(this.unsubscribeOnDestroy)
    ).subscribe(() => {
      const currentValue: string = this.ngControl.value.toString();
      const whitespace: string = ' ';
      if (currentValue.startsWith(whitespace) || currentValue.endsWith(whitespace)) {
        this.ngControl.control.patchValue(currentValue.trim());
      }
    });
  }

Answer 4

Though it's more than a year late, but you might want to try https://www.npmjs.com/package/ngx-trim-directive

It lies on a simple fact that Angular listens to input event to bring the view-to-model binding into being.

Demo: https://angular-86w6nm.stackblitz.io, editor: https://stackblitz.com/edit/angular-86w6nm

Answer 5

@ErVipinSharma I changed file src/input-trim.directive.ts, which you can find in above link to the github. In this file I removed method

@HostListener( 'input', ['$event.type', '$event.target.value'] )
onInput( event: string, value: string ): void {
    this.updateValue( event, value );
}

and added method

@HostListener('paste', ['$event', '$event.target'])
onPaste($event: any, target: any) {
    // do something when on paste event happens
}

Answer 6

Following directive could be used with Reactive-Forms to trim all form fields:

@Directive({
  selector: '[formControl], [formControlName]',
})
export class TrimFormFieldsDirective {
  @Input() type: string;

  constructor(@Optional() private formControlDir: FormControlDirective, 
              @Optional() private formControlName: FormControlName) {}

  @HostListener('blur')
  @HostListener('keydown.enter')
  trimValue() {
    const control = this.formControlDir?.control || this.formControlName?.control;
    if (typeof control.value === 'string' && this.type !== 'password') {
      control.setValue(control.value.trim());
    }
  }
}

Answer 7

I really liked this directive as it just auto-applies to almost everything:

import { Directive, forwardRef, HostListener } from '@angular/core';
import { DefaultValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';
const TRIM_VALUE_ACCESSOR: any = {
  provide: NG_VALUE_ACCESSOR,
  useExisting: forwardRef(() => TrimValueAccessorDirective),
  multi: true,
};
/**
 * The trim accessor for writing trimmed value and listening to changes that is
 * used by the {@link NgModel}, {@link FormControlDirective}, and
 * {@link FormControlName} directives.
 */
@Directive({
  // eslint-disable-next-line @angular-eslint/directive-selector
  selector: `
 input:not([type=checkbox]):not([type=radio]):not([type=password]):not([readonly]):not(.ng-trim-ignore)[formControlName],
 input:not([type=checkbox]):not([type=radio]):not([type=password]):not([readonly]):not(.ng-trim-ignore)[formControl],
 input:not([type=checkbox]):not([type=radio]):not([type=password]):not([readonly]):not(.ng-trim-ignore)[ngModel],
 textarea:not([readonly]):not(.ng-trim-ignore)[formControlName],
 textarea:not([readonly]):not(.ng-trim-ignore)[formControl],
 textarea:not([readonly]):not(.ng-trim-ignore)[ngModel],
 :not([readonly]):not(.ng-trim-ignore)[ngDefaultControl]'
 `,
  providers: [TRIM_VALUE_ACCESSOR],
})
export class TrimValueAccessorDirective extends DefaultValueAccessor {
  @HostListener('input', ['$event.target.value'])
  ngOnChange = (val: string) => {
    this.onChange(val.trim());
  };
  @HostListener('blur', ['$event.target.value'])
  applyTrim(val: string) {
    this.writeValue(val.trim());
  }
  writeValue(value: any): void {
    if (typeof value === 'string') {
      value = value.trim();
    }
    super.writeValue(value);
  }
}

From here: https://medium.com/@rm.dev/angular-auto-trim-your-input-string-using-angular-directive-5ae72b8cee9d