Angular 2: Apply Validator.required validation on some condition

Question

I have a angular 2 form wherein I have to make a field required on some condition like:

description:  [\'\', Validators.required]

This desc

Answer 1

If descReq needs to be evaluated at run-time (rather than when its initialized), then perhaps you should create a custom validator:

import { ValidatorFn, AbstractControl } from '@angular/forms';
interface ValidationResult {
    [key:string]:boolean;
}
function customValidator(condition: { required:boolean }) {
     return (control: AbstractControl) :ValidationResult  => {
         return condition.required && 
             (control.value == undefined || 
              control.value == null || 
              control.value.trim() =='') ? 
              {
                 'required': true
              }: null;

       }

}

Use like this:

description:  ['', customValidator(this.reqd)]

where reqd has been initialized earlier, and maybe even data-bound:

reqd = { required: false };