Angular2: Validate form without defining error messages at each input?

Question

I want validate form in angular2. I learn some document, and it will be define like this:

<form [ngFormModel]="form">
        <input type="text" ngControl="username" />

        <p *ngIf="username.pending">Fetching data from the server...</p>

        <div *ngIf="username.dirty && !username.valid && !username.pending">
          <p *ngIf="username.errors.required">Username is required.</p>
          <p *ngIf="username.errors.startsWithNumber">Your username can't start with a number</p>
          <p *ngIf="username.errors.usernameTaken">This username is taken</p>
        </div>

        <button (click)="submitData()" [disabled]="!form.valid" class="btn btn-primary">Sumbit data</button>
</form>

constructor(private builder: FormBuilder) {

    this.username = new Control(
        "", 
        Validators.compose([Validators.required, UsernameValidator.startsWithNumber]),
        UsernameValidator.usernameTaken
    );

    this.form = builder.group({
        username:  this.username
    });
}

With each input I need to define many error messages. I think it's not good.
I want like jquery.validate, I just define input and the error messages will be auto render, like this

<input required name="username" maxlength='8' pattern="^(?!\s|.*\s$).*$" ...> 

Answer 1

To reduce your code one approach could be to write a component.

Which will handle all the condition checkings and error messages

This guy did a nice job here of implementing and explaining it.

---

HTML with Component would look like this

<input ngControl="email" id="email" />
<control-messages control="email"></control-messages>

and all the dirty work would go inside control-messages component.