MouseEvent.altKey

The MouseEvent.altKey read-only property is a Boolean that indicates whether the alt key was pressed or not when a given mouse event occurs.

Be aware that the browser can't always detect the alt key on some operating systems. On some Linux variants, for example, a left mouse click combined with the alt key is used to move or resize windows.

var altKeyPressed = instanceOfMouseEvent.altKey

A Boolean, where true indicates that the key is pressed, and false indicates that the key is not pressed.

This example logs the altKey property when you trigger a click event.

<p>Click anywhere to test the <code>altKey</code> property.</p>
<p id="log"></p>

let log = document.querySelector('#log');
document.addEventListener('click', logKey);

function logKey(e) {
  log.textContent = `The alt key is pressed: ${e.altKey}`;
}

• MouseEvent