Typescript input onchange event.target.value

Question

In my react and typescript app, I use: onChange={(e) => data.motto = (e.target as any).value}.

How do I correctly define the typings for the class, s

Answer 1

An alternative that has not been mentioned yet is to type the onChange function instead of the props that it receives. Using React.ChangeEventHandler:

const stateChange: React.ChangeEventHandler<HTMLInputElement> = (event) => {
    console.log(event.target.value);
};

Answer 2

Generally event handlers should use e.currentTarget.value, e.g.:

onChange = (e: React.FormEvent<HTMLInputElement>) => {
    const newValue = e.currentTarget.value;
}

You can read why it so here (Revert "Make SyntheticEvent.target generic, not SyntheticEvent.currentTarget.").

UPD: As mentioned by @roger-gusmao ChangeEvent more suitable for typing form events.

onChange = (e: React.ChangeEvent<HTMLInputElement>)=> {
   const newValue = e.target.value;
}

Answer 3

Here is a way with ES6 object destructuring, tested with TS 3.3.
This example is for a text input.

name: string = '';

private updateName({ target }: { target: HTMLInputElement }) {
    this.name = target.value;
}

Answer 4

  function handle_change(
    evt: React.ChangeEvent<HTMLInputElement>
  ): string {
    evt.persist(); // This is needed so you can actually get the currentTarget
    const inputValue = evt.currentTarget.value;

    return inputValue
  }

And make sure you have "lib": ["dom"] in your tsconfig.

Answer 5

This is when you're working with a FileList Object:

onChange={(event: React.ChangeEvent<HTMLInputElement>): void => {
  const fileListObj: FileList | null = event.target.files;
  if (Object.keys(fileListObj as Object).length > 3) {
    alert('Only three images pleaseeeee :)');
  } else {
    // Do something
  }

  return;
}}

Answer 6

The target you tried to add in InputProps is not the same target you wanted which is in React.FormEvent

So, the solution I could come up with was, extending the event related types to add your target type, as:

interface MyEventTarget extends EventTarget {
    value: string
}

interface MyFormEvent<T> extends React.FormEvent<T> {
    target: MyEventTarget
}

interface InputProps extends React.HTMLProps<Input> {
    onChange?: React.EventHandler<MyFormEvent<Input>>;
}

Once you have those classes, you can use your input component as

<Input onChange={e => alert(e.target.value)} />

without compile errors. In fact, you can also use the first two interfaces above for your other components.