Angular 2 custom validator with parameters

Question

How do I create let's say my own maxLength validator in Angular 2? All examples I could find use validators similar to 'required' one meaning that they already know the rules. They only accept one param - the control itself. How do I pass more parameters?

Here's the sample validator I have. How do I modify it to pass number 5 as a parameter?

export class MyValidators {
    static minValue(control:Control): {[s: string]: boolean} {
        var num = +control.value;
        if (isNaN(num) || num < 5 ) { return {"minValue": true}; }
        return null;
    }
}

score 43 · Accepted Answer · edited Sep 16 '17 at 11:06

43

Here is a sample. It's a min value validator where you pass in a number to validate.

import {Control} from 'angular2/common';

export const minValueValidator = (min:number) => {
  return (control:Control) => {
    var num = +control.value;
    if(isNaN(num) || num < min){
      return {
         minValue: {valid: false}
      };
    }
    return null;
  };
};

More details can be found in the Custom Validators official documentation page.

edited Sep 16 '17 at 11:06

Francesco Borzi

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answered Apr 21 '16 at 02:18

TGH

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`minValueValidator = (min: number) => {}` would be better ?! – Ankit Singh Apr 21 '16 at 04:33
That works. Thank you! I also added isNaN check and replaced 'export const' with 'static' to make it a member of a class. – rook Apr 21 '16 at 16:26
Updated to include NAN check – TGH Apr 21 '16 at 16:39
14

how can i pass variable value to this validator ? i notice it always expects string constant like and won't let me do – d-man Jan 06 '17 at 17:43
This won't work with the AOT compiler since lambda isn't supported: https://angular.io/guide/aot-compiler – Sjoerd de Wit Sep 24 '18 at 12:31

score 4 · Answer 2 · answered Mar 07 '17 at 14:39

The minValueValidator example basically shows that you can use a factory for your custom validator so it will be something like this:

static minValue = (num: Number) => {
    return (control:Control) => {
         var num = control.value;
         if (isNaN(num) || num < 5 ) { return {"minValue": true}; }
         return null;
    }
}

In my case I use FormControl not Control

import { FormControl } from '@angular/forms';

score 2 · Answer 3 · answered Dec 02 '19 at 16:25

Another solution here that uses a little more Angular nuance:

  static minValue(min: number): ValidatorFn {
    return (control: AbstractControl): ValidationErrors | null => {
      if (control.value == null || control.value == '') {
        //avoid validation if empty, we are not testing for required here
        return null;
      }
      const errors: ValidationErrors = {};
      let num = +control.value;
      if (isNaN(num) || num < min) {
        errors.isLessThanMin = {
          message: `Number must be greater that ${min}`
        };
      }
      return Object.keys(errors).length ? errors : null;
    };
  }

Now you have a much more reusable html error message

<div *ngIf="control.errors.isLessThanMin>{{control.errors.isLessThanMin.message}}</div>

Angular 2 custom validator with parameters

3 Answers3

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