What Typescript type is a change event? (In Angular)

Question

I'm trying to figure out what Typescript type a change event is used in an Angular project.

The code is something simple like this:

file-upload.component.html

<input type="file" (change)="onChange($event)"/>

file-upload.ts

public onChange(event: Event): void {
  if (event.target.files && event.target.files.length) {
    const [file] = event.target.files;
    console.log(file);
  }
}

Typing the event as Event gives me the following Typescript linting error:

Property 'files' does not exist on type 'EventTarget'

What should I be typing this if not Event?

Answer 1

It is an event. But you're going to have to cast the const you're using as an HTMLInputElement.

public onChange(event: Event): void {
  if ((event.target as HTMLInputElement).files && (event.target as HTMLInputElement).files.length) {
    const [file] = event.target.files;
  }
}

The only other way is going to be to suppress the error with tsignore. In react, flow, they have a type SyntheticEvent that you can type this particular case as to get around it but angular doesn't have a real equivalent.

Answer 2

public onChange(event: Event): void {
    const input = event.target as HTMLInputElement;

    if (!input.files?.length) {
        return;
    }

    const file = input.files[0];
    console.log(file);
}

Answer 3

You just have to write this before doing anything with your event:

if (!(event.target instanceof HTMLInputElement)) return;

Typescript will then know that your event.target is an instance of HTMLInputElement and it will stop yelling at you.