The KeyboardEvent.altKey read-only property is a Boolean indicates if the alt key (Option or ⌥ on OS X) was pressed (true) or not (false) when the event occured.
Syntax
var altKeyPressed = instanceOfKeyboardEvent.altKey
Examples
<html>
<head>
<title>altKey example</title>
<script type="text/javascript">
function showChar(e){
alert(
"Key Pressed: " + String.fromCharCode(e.charCode) + "\n"
+ "charCode: " + e.charCode + "\n"
+ "ALT key pressed: " + e.altKey + "\n"
);
}
</script>
</head>
<body onkeypress="showChar(event);">
<p>
Press any character key,
with or without holding down the ALT key.<br />
You can also use the SHIFT key together with the ALT key.
</p>
</body>
</html>
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