Angular 7 Reactive Forms Cannot read property 'controls' of undefined

Question

I am using ReactiveForms in Angular v7.

Template

<div class="login__container">
    <div class="login__form">
        <form novalidate [formGroup]="loginForm" (ngSubmit)="onSubmit()">
            <div class="field">
                <p class="control">
                    <input class="input" type="text" placeholder="Username" formControlName="username" [ngClass]="{ 'is-invalid': submitted && f.username.errors }">
                </p>
            </div>
            <div class="field">
                <p class="control">
                    <input class="input" type="password" placeholder="Password" formControlName="password" [ngClass]="{ 'is-invalid': submitted && f.password.errors }">
                </p>
            </div>
            <div class="field">
                <p class="control">
                    <button class="button is-success" [disabled]="!loginForm.valid">
                        Login
                    </button>
                </p>
            </div>
        </form>
    </div>
</div>

Component

import { Component, OnInit } from '@angular/core'
import { FormBuilder, FormGroup, Validators } from '@angular/forms'

@Component({
    selector: 'app-login-component',
    templateUrl: './login.component.html',
    styleUrls: ['./login.component.scss']
})
export class LoginComponent implements OnInit {
    loginForm: FormGroup
    submitted = false

    constructor(private fB: FormBuilder) {}

    ngOnInit() {
        this.loginForm = this.fB.group({
            username: ['', Validators.required],
            password: ['', Validators.required]
        })
    }

    // convenience getter for easy access to form fields
    get f() {
        return this.loginForm.controls
    }

    onSubmit() {
        this.submitted = true

        // stop here if form is invalid
        if (this.loginForm.invalid) {
            return
        }

        console.log(this.loginForm.value)
    }
}

When I go to this route, I have a console error

ERROR TypeError: Cannot read property 'controls' of undefined
    at Object.get [as f] (http://localhost:4200/main.js:257:35)
    at http://localhost:4200/vendor.js:92667:9
    at Array.forEach (<anonymous>)
    at deepFreeze (http://localhost:4200/vendor.js:92664:33)
    at http://localhost:4200/vendor.js:92670:7
    at Array.forEach (<anonymous>)
    at deepFreeze (http://localhost:4200/vendor.js:92664:33)
    at http://localhost:4200/vendor.js:92670:7
    at Array.forEach (<anonymous>)
    at deepFreeze (http://localhost:4200/vendor.js:92664:33)

I cannot work out why this happening, the validation around the submit button appears to be working, so I can only assume the fields are being referenced correctly. I suspect the issue is coming from the convenience getter set within the component, however I cannot see what is wrong with this as autocomplete is providing me with the values I expect.

Solution 1

Instead of the convenience method you are using, you could simply reference the field like

[ngClass]="{ 'is-invalid': submitted && loginForm.controls['username'].errors }"

It would then be a case of showing an error message if you so wish using

<div *ngIf="submitted && loginForm.controls['username'].hasError('required')" class="error-message">Username is required</div>

I am not clear on what benefit your current approach is affording you over something straight forward such as this.

Solution 2

Should be pretty easy to fix by checking loginForm in html.

<div class="login__container" *ngIf="loginForm"> <!-- Check here -->
    <div class="login__form">
        <form novalidate [formGroup]="loginForm" (ngSubmit)="onSubmit()">
            <div class="field">
                <p class="control">
                    <input class="input" type="text" placeholder="Username" formControlName="username" [ngClass]="{ 'is-invalid': submitted && f.username.errors }">
                </p>
            </div>
            <div class="field">
                <p class="control">
                    <input class="input" type="password" placeholder="Password" formControlName="password" [ngClass]="{ 'is-invalid': submitted && f.password.errors }">
                </p>
            </div>
            <div class="field">
                <p class="control">
                    <button class="button is-success" [disabled]="!loginForm.valid">
                        Login
                    </button>
                </p>
            </div>
        </form>
    </div>
</div>

Comments

[Ajay Ojha]

check first 'this.loginForm' is undefined or not in f method. or else you can use loginForm.controls.username.errors in the HTML.

[shuk]

Another option is to pass the formBuilder from ngOnInit cycle to constructor cycle

[Jota.Toledo]

As it is, Im not able to reproduce your issue stackblitz.com/edit/angular-lpstaz

[Jota.Toledo]

As @OmerShukar mentioned, you could try by instantiating the form in the constructor

[Harry Blue]

Using the constructor did not help, it also doesn’t appear to follow the docs set out by Angular.

[Jota.Toledo]

This wont make a difference