Angular Directive Example to Format Value to Currency

The following is an example of an Angular 6 directive that format input value to currency when losing focus. It uses NgModel for value binding and CurrencyPipe for the formatter.

import { Directive } from '@angular/core';
import { NgModel } from '@angular/forms';
import { CurrencyPipe } from '@angular/common';

@Directive({
  selector: '[ngModel][my-directive]',
  providers: [NgModel, CurrencyPipe],
  host: {
    '(blur)': 'onInputChange($event)'
  } 
})
export class MyDirective {

  constructor(private model: NgModel, private currencyPipe: CurrencyPipe) { }

  onInputChange($event) {
    var value = $event.target.value;
    if (!value) return;

    var plainNumber: number;
    var formattedValue: string;


    var decimalSeparatorIndex = value.lastIndexOf('.'); 
    if (decimalSeparatorIndex > 0) {
      // if input has decimal part
      var wholeNumberPart = value.substring(0, decimalSeparatorIndex);
      var decimalPart = value.substr(decimalSeparatorIndex + 1);
      plainNumber = parseFloat(wholeNumberPart.replace(/[^\d]/g, '') + '.' + decimalPart)
    } else {
      // input does not have decimal part
      plainNumber = parseFloat(value.replace(/[^\d]/g, ''));
    }

    if (!plainNumber) {
      formattedValue = '';
    }
    else {
      formattedValue = this.currencyPipe.transform(plainNumber.toFixed(2), "USD", "symbol-narrow");
    }

    this.model.valueAccessor.writeValue(formattedValue);
  }
}

Then to use it on HTML part:

<input name="productPrice" [(ngModel)]="price" my-directive />

Angular Directive Example to Allow Certain Values

Below is an example of an Angular 6 Directive. This directive detects changes in NgModel as user enters in input value and only allows specific value to be entered while rejecting the others.

import { Directive } from '@angular/core';
import { NgModel } from '@angular/forms';

@Directive({
  selector: '[ngModel][my-directive]',
  providers: [NgModel],
  host: {
    '(ngModelChange)': 'onInputChange($event)'
  } 
})
export class MyDirective {

  constructor(private model: NgModel) { }

  onInputChange(value) {
    console.log(value);
    
    this.model.valueAccessor.writeValue(value.replace(/[^\d\.\,\s]+/g, ''));
  }
}

Then to use it on HTML part:

<input name="productPrice" [(ngModel)]="price" my-directive />