Type the onKeyDown event in React (TypeScript)

Type the onKeyDown event in React (TypeScript) #

Use the React.KeyboardEvent<HTMLElement> type to type the onKeyDown event in React. The KeyboardEvent interface is used for onKeyDown events. You can access the value of the key pressed by the user as event.key.

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import React from 'react';

const App = () => {
  // 👇️ type event as React.KeyboardEvent<HTMLElement>
  const handleKeyDown = (event: React.KeyboardEvent<HTMLElement>) => {
    console.log(event.key);
  };

  return (
    <div>
      <input
        type="text"
        id="message"
        name="message"
        defaultValue=""
        onKeyDown={handleKeyDown}
      />
    </div>
  );
};

export default App;

We typed the event as React.KeyboardEvent<HTMLElement> because the KeyboardEvent type is used for onKeyDown events in React.

However, we could have been more specific when typing the event.

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const App = () => {
  // 👇️ onKeyDown event is written inline
  // hover over the `event` parameter with your mouse
  return (
    <div>
      <input
        type="text"
        id="message"
        name="message"
        defaultValue=""
        onKeyDown={event => console.log(event)}
      />
    </div>
  );
};

export default App;

TypeScript is able to infer the type of the event when it's written inline.

This is very useful because it works with all events. Simply write a "mock" implementation of your event handler inline and hover over the event parameter to get its type.

Now that we know that the correct type for the onKeyDown event in the example is React.KeyboardEvent<HTMLInputElement>, we can extract our handler function.

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import React from 'react';

const App = () => {
  // 👇️ type event correctly
  const handleKeyDown = (event: React.KeyboardEvent<HTMLInputElement>) => {
    console.log(event.key);
  };

  return (
    <div>
      <input
        type="text"
        id="message"
        name="message"
        defaultValue=""
        onKeyDown={handleKeyDown}
      />
    </div>
  );
};

export default App;

The key property on the KeyboardEvent object returns the value of the key that was pressed by the user.

The type we passed to the KeyboardEvent generic is HTMLInputElement because we attached the onKeyDown event to an input element, however you could be attaching the event to a different element.

Some commonly used types are: HTMLInputElement, HTMLButtonElement, HTMLAnchorElement, HTMLImageElement, HTMLTextAreaElement, HTMLSelectElement, etc.

As long as you write the event handler function inline and hover over the event parameter, TypeScript will be able to infer the event's type.