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The truth about Angular form

Jose Álvarez
・2 min read

introdution

In this article i want to explain how to use angular forms directives in the right way, because i've observed that is not already clear how to use it correctly or what is the diferent about use template forms and built our owned form whith FormBuilder class. I am not going to enter in how to create a form in angular only i want to explain the interesting things.

explanation

I'm going to start with something very simple but could be doubs about this.

The question is: What happens when we use <form #f="ngForm" ... ?

Someone could think that we're referencing our form, this could be true, but in reality more things are happening behind the scenes.

The truth about this is that when we import FormsModule automatically NgForm is avalilable in our view, this means that NgForm is automatically attached to any <form> in our view and is not necessary add explicitly ngForm as an attribute.

Answering the question posed, when we use #f="ngForm" in a form tag in reality we're creating a FormGroup ! where f is the type FormGroup, this is so because this syntax says that we want to create a local variable for this view but, where did ngForm cames from ? it came from the NgForm directive.

At this moment you could think, ok f variable is a FormGroup, if you remenber a FormGroup is composed by FormControls and, where are they in our form ? Now comes into play NgModel directive.

When we use ngModel with no attribute vslue we are specifying that at first we want a one-way data binding, and this is important we want to create a FormControl on this form with the name same as name attribute. NgModel creates a new FormControl that is automatically added to the parent FromGroup.

Now we can build our form like this:

<!-- Creates a FormGroup-->
<form #f="ngForm" (ngSubmit)="onSubmit(f.value)">
  <!-- Creates a FormControl with name email -->
  <input name="email" type="email"  ngModel >
  <!-- Creates a FormControl with name password -->
  <input name="password" type="password" ngModel >
</form>
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Conclusion

In this simple way we can create a valid form in Angular using template forms, but create form with this way have some limitations, for example what happens if we want validate the password input, we cant specify validators for FormControls and neither we can't listen the form events. If we aren't want do special stuff template form could be a great solution.

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