Angular Reactive form validation

Question

I'm working with a Reactive form and I have noticed in some tutorials they do the following:

HTML

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<input type="text" formControlName="firstName" required>
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TS

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firstName: ['', Validators.required]
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QUESTION:

Why do I need to specify "required" in the HTML if I just do it in the TS file it works fine?

Answer 1

Actually, Angular mention something about that here:

Caution: Use these HTML5 validation attributes in combination with the built-in validators provided by Angular's reactive forms. Using these in combination prevents errors when the expression is changed after the template has been checked.