Angular : This is a custom directive to remove matching regex pattern from ngModel inputs

regex-remove.ts

import { Directive, HostListener, Input, OnChanges, Optional } from '@angular/core';
import { NgModel } from '@angular/forms';

/**
 * @description
 * 
 * This is a custom directive to remove matching regex pattern from ngModel inputs
 * 
 * eg:
 *    (will remove character matching the default regular expression present in the directive)
 *   1. <input type="text" [(ngModel)]="componentVaribale" name="name1" appRmPattern>
 *    (will remove character matching the given regular expression)
 *   2. <input type="text" [(ngModel)]="componentVaribale" name="name2" appRmPattern="/^[abc]/">
 */
@Directive({
  selector: '[appRmPattern]'
})
export class RmPatternDirective implements OnChanges {

  private pattern = /[^\w\d\s\_\-]/gm; // default pattern
  @Input('appRmPattern') userPattern: string;
  constructor(@Optional() public model: NgModel) { 
     if (!model){throw new Error ("myCustomDirective requires ngModel.");}
  }

  ngOnChanges() {
    if (this.userPattern) {
      var regParts = this.userPattern.match(/^\/(.*?)\/([gim]*)$/);
      if (regParts) {
        // pattern with delimiters and modifiers
        this.pattern = new RegExp(regParts[1], regParts[2]);
      } else {
        // pattern without delimiters
        this.pattern = new RegExp(this.userPattern);
      }
    }
  }

  @HostListener('input', ["$event"]) onUserInput(event) {
    event.target.value = event.target.value.replace(this.pattern, '');
    if (this.model) {
      this.model.update.emit(event.target.value);
    }

  }

}