Provide ability to transform value before write

[dev054]

🚀 feature request

There are some cases where we should allow only letters (say full name) and as the user types, we transform to uppercase.

Describe the solution you'd like

I'd like to have an option to transform value before masking.

<!-- the name could be any, it's just an idea ->
<input matInput formControlName="test" mask="S*" [transformer]="transformerFn">

transformerFn = (value: string) => value.toLocaleUppercase();

this.formGroup.get('test').valueChanges.subscribe(console.log); // fired only once, with the value uppercased

Describe alternatives you've considered

Well, while we could add a directive to perform its transformation by listening input event, but has the following drawback:

• The valueChanges/(change) would be emitted twice. One for the value masked and another for the value uppercased. To try workaround this you could setValue passing { emitEvent: false }, however it would be a problem, because you'll have an outdated value in valueChanges/(change);

[andriikamaldinov1]

@dev054 Thanks for using Ngx-mask. We add two new function "inputTransformFn" and "outputTransformFn".
It example with your case - https://stackblitz.com/edit/stackblitz-starters-wj3nvw?file=src%2Fmain.ts