Keyboard Events

Introduction to JavaScript keyboard events

When you interact with the keyboard, the keyboard events are fired. There are three main keyboard events:

  • keydown – fires when you press a key on the keyboard and fires repeatedly while you’re holding down the key.

  • keyup – fires when you release a key on the keyboard.

  • keypress – fires when you press a character keyboard like a,b, or c, not the left arrow key, home, or end keyboard, … The keypress also fires repeatedly while you hold down the key on the keyboard.

The keyboard events typically fire on the text box, though all elements support them.

When you press a character key once on the keyboard, three keyboard events are fired in the following order:

  1. keydown

  2. keypress

  3. keyup

Both keydown and keypress events are fired before any change is made to the text box, whereas the keyup event fires after the changes have been made to the text box. If you hold down a character key, the keydown and keypress are fired repeatedly until you release the key.

When you press a non-character key, the keydown event is fired first followed by the keyup event. If you hold down the non-character key, the keydown is fired repeatedly until you release the key.

Handling keyboard events

To handle a keyboard event, you follow these steps:

  • First, select the element on which the keyboard event will fire. Typically, it is a text box.

  • Then, use the element.addEventListener() to register an event handler.

Suppose that you have the following text box with the id message:

<input type="text" id="message">Code language: HTML, XML (xml)

The following illustrates how to register keyboard event listeners:

let msg = document.getDocumentById('#message');

msg.addEventListener("keydown", (event) => {
    // handle keydown
});

msg.addEventListener("keypress", (event) => {
    // handle keypress
});

msg.addEventListener("keyup", (event) => {
    // handle keyup
});Code language: PHP (php)

If you press a character key, all three event handlers will be called.

The keyboard event properties

The keyboard event has two important properties: key and code. The key property returns the character that has been pressed whereas the code property returns the physical key code.

For example, if you press the z character key, the event.key returns z and event.code returns KeyZ.

See the following example:

<!DOCTYPE html>
<html>
<head>
    <title>JavaScript Keyboard Events: Key/Code</title>
</head>
<body>
    <input type="text" id="message">

    <script>
        let textBox = document.getElementById('message');
        textBox.addEventListener('keydown', (event) => {
            console.log(`key=${event.key},code=${event.code}`);

        });
    </script>
</body>
</html>Code language: HTML, XML (xml)

If you type character z, you will see the following message:

key=z,code=KeyZ

How it works:

  • First, select the text box with the id message by using the getElementById() method.

  • Then, register a keydown event listener and log the key and code of the key that has been pressed.

Summary

  • When you press a character key on the keyboard, the keydown, keypress, and keyup events are fired sequentially. However, if you press a non-character key, only the keydown and keyup events are fired.

  • The keyboard event object has two important properties: key and code properties that allow you to detect which key has been pressed.

  • The key property returns the value of the key pressed while the code represents a physical key on the keyboard.

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