Angular 4 - validator custom function this is undefined

Question

I'm building an app with component FormComponent. inside I'm using reactive forms module from angular core and create a custom validator. the function is calling another function by using this - as I supposed it will refer to the FormComponent, but it refers to be 'undefined' (?)

The code in onInit defines the FormGroup and FormControl and outside of it defines the functions

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, Validators } from '@angular/forms';
import { Router } from '@angular/router';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-form',
  templateUrl: './form.component.html',
  styleUrls: ['./form.component.css']
})
export class FormComponent implements OnInit {

  formInsurance:FormGroup;
  private id:FormControl;


  constructor(){}


  ngOnInit() {

    this.id = new FormControl('',[
      Validators.required,
      Validators.minLength(3),
      Validators.maxLength(10),
      Validators.pattern('^[0-9]+(-[0-9]+)+$|^[0-9]+$'),
      this.foo
    ]);


    this.formInsurance = new FormGroup({
      id:this.id      
    })


  }


  foo(control:FormControl){
  this.boo();
  if(control.value){
    return {
      objToReturn: {
          returned: name
      }
    };
  }
  return null
}

boo(){
  console.log('boo')

}

}

Tagliatelle

It's written outside onInit, but I guess it is called on the onInit scope because this is when the form control validators initial – Tagliatelle

yes sorry , i have just seen it – Peggi

Answer 1

The context in the foo method when called from within the FormControl is not referencing the FormComponent.

You can do the following to fix this behavior using bind to set the context yourself:

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, Validators } from '@angular/forms';
import { Router } from '@angular/router';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-form',
  templateUrl: './form.component.html',
  styleUrls: ['./form.component.css']
})
export class FormComponent implements OnInit {

  formInsurance:FormGroup;
  private id:FormControl;


  constructor(){}


  ngOnInit() {

    const id = new FormControl('',[
      Validators.required,
      Validators.minLength(3),
      Validators.maxLength(10),
      Validators.pattern('^[0-9]+(-[0-9]+)+$|^[0-9]+$'),
      this.foo.bind(this)
    ]);

    this.id = id;

    this.formInsurance = new FormGroup({
      id
    })
  }


  foo(control:FormControl) {
    this.boo();
    if(control.value){
        return {
          objToReturn: {
              returned: name
          }
        };
      }
    return null
  }

  boo(){
    console.log('boo')

  }
}

Uni

Thank you! This was annoying to deal with. – Rachellerachis

Answer 2

And of course, the other alternative is the arrow function, which auto-binds to the this context:

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, Validators, ValidationErrors } from '@angular/forms';
import { Router } from '@angular/router';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-form',
  templateUrl: './form.component.html',
  styleUrls: ['./form.component.css']
})
export class FormComponent implements OnInit {

  formInsurance:FormGroup;
  private id:FormControl;

  constructor() {}

  ngOnInit() {
    this.id = new FormControl('',[
      Validators.required,
      Validators.minLength(3),
      Validators.maxLength(10),
      Validators.pattern('^[0-9]+(-[0-9]+)+$|^[0-9]+$'),
      this.foo
    ]);

    this.formInsurance = new FormGroup({
      id:this.id      
    })
  }

  foo = (control: FormControl): ValidationErrors => {
    this.boo();
    if (control.value) {
      return {
        objToReturn: {
          returned: name
        }
      };
    }
    return null
  }

  boo() {
    console.log('boo')
  }
}

Lir

Thanks!! This helped me when this.foo.bind(this) didn't work. – Plataea

Answer 3

You can return the needed function, take what you want from this as a parameter and return the function that you want. That way it's cleaner because often times you'd only need one value from this

in you example, it would look like this:

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, Validators } from '@angular/forms';
import { Router } from '@angular/router';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-form',
  templateUrl: './form.component.html',
  styleUrls: ['./form.component.css']
})
export class FormComponent implements OnInit {

  formInsurance: FormGroup;
  private id: FormControl;


  constructor() { }

  ngOnInit() {

    this.id = new FormControl('', [
      Validators.required,
      Validators.minLength(3),
      Validators.maxLength(10),
      Validators.pattern('^[0-9]+(-[0-9]+)+$|^[0-9]+$'),
      this.foo(this.boo)
    ]);


    this.formInsurance = new FormGroup({
      id: this.id
    })
  }

  foo(boo) {
    return (control: FormControl) => {
      boo();
      if (control.value) {
        return {
          objToReturn: {
            returned: name
          }
        };
      }
      return null
    }
  }

  boo() {
    console.log('boo')
  }

Pickpocket