Angular Reactive Forms：在值改变之前检测用户输入

Question

I know that you can use the valueChanges observable in Angular Reactive Forms to detect if a value in the input field has already changed:

inputControl.valueChanges.subscribe(() => {
    // fires when the input value has actually changed
});

However, is there a way to subscribe to an observable of when the user has pressed a key, before the value changes in the input?

I need to do this so I can apply dynamic validation, for example:

1. User presses a key
2. I need to know what that key is before I apply validation
3. Validation then works on the changed value of the input

Answer 1

is there a way to subscribe when the user has pressed a key, before the value changes in the input?

onkeyup event :

 <input formControlName="yourcontrol" (keyup)="onKeyUp($event)">

EDIT :

You need subscribe to event keyup on your AbstractControl elememnt .

see the stackblitz

You could also create a directive to access your element using ElementRef regarding what your requirements are.