The MouseEvent.altKey read-only property is a Boolean indicates if the alt key was pressed (true) or not (false) when the event occurred.
var altKeyPressed = instanceOfMouseEvent.altKey
<html>
<head>
<title>altKey example</title>
<script type="text/javascript">
document.addEventListener('click', function(e) {
console.log('Is Alt/Option key pressed?', e.altKey);
})
</script>
</head>
<body>
<p>
Click anywhere on the page and open your developer console to see the results.
</p>
</body>
</html> | Specification | Status | Comment |
|---|---|---|
| Document Object Model (DOM) Level 3 Events Specification The definition of 'MouseEvent.altkey' in that specification. | Obsolete | No change from Document Object Model (DOM) Level 2 Events Specification. |
| Document Object Model (DOM) Level 2 Events Specification The definition of 'MouseEvent.altkey' in that specification. | Obsolete | Initial definition. |
| Desktop | ||||||
|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | |
| Basic support | Yes | Yes | Yes | Yes | Yes | Yes |
| Mobile | |||||||
|---|---|---|---|---|---|---|---|
| Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | iOS Safari | Samsung Internet | |
| Basic support | ? | ? | Yes | ? | ? | ? | ? |
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https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/altKey