Angular template validation form

Question

I am working on the form validation. I am using template-driven validation form whose coding is below. Its working fine now but when I try to add #username = "ngModel" and #password = "ngModel" in input to create validation classes it's showing me an error. Please find the error also.

<div class="container">
  <div class="row">
    <div class="centering text-center">
      <div class="login-cont col-md-4 col-md-offset-4 vcenter">
        <form id="login_form" name="login-form" #f="ngForm"  role="form" (ngSubmit)="f.form.valid && login()" novalidate>

          <input id="username" [(ngModel)]="username"  name="username"  required  class="form-control"  type="text"   placeholder="Username" >
<input id="userPassword" class="form-control"  required type="password" name="userPassword" required placeholder="Password" [(ngModel)]="password" >
<button type="submit" class="btn login-btn">Login</button>
</form>
</div>
</div>
</div>
</div>

---

 Cannot assign to a reference or variable!
    at _AstToIrVisitor.visitPropertyWrite (webpack-internal:///../../../compiler/esm5/compiler.js:26226:23)
    at PropertyWrite.visit (webpack-internal:///../../../compiler/esm5/compiler.js:4803:24)
    at convertActionBinding (webpack-internal:///../../../compiler/esm5/compiler.js:25676:45)
    at eval (webpack-internal:///../../../compiler/esm5/compiler.js:28166:22)
    at Array.forEach (<anonymous>)
    at ViewBuilder._createElementHandleEventFn (webpack-internal:///../../../compiler/esm5/compiler.js:28162:18)
    at nodes.(anonymous function) (webpack-internal:///../../../compiler/esm5/compiler.js:27581:27)
    at eval (webpack-internal:///../../../compiler/esm5/compiler.js:28107:22)
    at Array.map (<anonymous>)
    at ViewBuilder._createNodeExpressions (webpack-internal:///../../../compiler/esm5/compiler.js:28106:56)

---

This is what I tried but it gives me an error

   <input id="username" class="form-control"  type="text" required  name="username" placeholder="Username" [(ngModel)]="username" minlength="4"  #names="ngModel">


          <div *ngIf="names.invalid && (names.dirty || names.touched)"
               class="alert alert-danger">
          </div>
            <div *ngIf="names.errors.required">
              Name is required.
            </div>

            <div *ngIf="names.errors.minlength">
              Name must be at least 4 characters long.
            </div>

Answer 1

You are getting error because of your variable name and local variable name both are same

username is a variable that you are assigning to [(ngModel)]='username' , at the same time you are also trying to make local variable #username

Use different name like #username2 or #password2 , will solve your problem.

For more details read :

https://scotch.io/tutorials/using-angular-2s-template-driven-forms

Answer 2

FormBuilder can help you.

export class MyComp {
  myForm: FormGroup;
  constructor(private fb: FormBuilder) {
    this.myForm = fb.group({
      username: ['', [Validator.required]],
      userPassword: ['', [Validator.required]]
    });
  }

<div class="container">
  <div class="row">
    <div class="centering text-center">
      <div class="login-cont col-md-4 col-md-offset-4 vcenter">
        <form [formGroup]="myForm" id="login_form"(submit)="login()">
          <input id="username" class="form-control" type="text" placeholder="Username" >
          <input id="userPassword" class="form-control" type="password" placeholder="Password">
          <button type="submit" class="btn login-btn" [disabled]="myForm.invalid">Login</button>
        </form>
      </div>
    </div>
  </div>
</div>