The altkey property is used to show whether ALT key is pressed or not when key event was triggered.
Example
You can try to run the following code to learn how to implement altKey property in JavaScript.
<!DOCTYPE html>
<html>
<body>
<input type = "text" onkeydown = "funcAltKey(event)">
<div id = "res"> Press any key </div>
<script>
function funcAltKey(event) {
var val = document.getElementById("res");
if (event.altKey) {
val.innerHTML = "ALT key: Pressed";
} else {
val.innerHTML = "ALT key: NOT Pressed";
}
}
</script>
</body>
</html>