UIEvent.which

Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

The UIEvent.which read-only property of the UIEvent interface returns a number that indicates which button was pressed on the mouse, or the numeric keyCode or the character code (charCode) of the key pressed on the keyboard.

Syntax

var result = event.which;

Return value

Return value for `KeyboardEvent`

event.which contains the numeric code for a particular key pressed, depending on whether an alphanumeric or non-alphanumeric key was pressed. Please see deprecated KeyboardEvent.charCode and KeyboardEvent.keyCode for more details.

Note: Consider KeyboardEvent.key or KeyboardEvent.code for new code.

Return value for `MouseEvent`

A number representing a given button:

0: No button
1: Left button
2: Middle button (if present)
3: Right button

For a mouse configured for left-handed use, the button actions are reversed. In this case, the values are read from right to left.

Note: Consider MouseEvent.button for new code.

Example

<html>
<head>
<title>charCode/keyCode/which example</title>

<script type="text/javascript">

function showKeyPress(evt) {
alert("onkeypress handler: \n"
      + "keyCode property: " + evt.keyCode + "\n"
      + "which property: " + evt.which + "\n"
      + "charCode property: " + evt.charCode + "\n"
      + "Character Key Pressed: "
      + String.fromCharCode(evt.charCode) + "\n"
     );
}

function keyDown(evt) {
alert("onkeydown handler: \n"
      + "keyCode property: " + evt.keyCode + "\n"
      + "which property: " + evt.which + "\n"
     );
}

</script>
</head>

<body
 onkeypress="showKeyPress(event);"
 onkeydown="keyDown(event);"
>

<p>Please press any key.</p>

</body>
</html>

Specifications

Specification
UI Events # dom-uievent-which

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`which`	1	79 12-79 Only supported for `KeyboardEvent` and `MouseEvent`, not all `UIEvent` objects.	1 On `mousemove` events, the `which` property is incorrectly always set to `1`.	9 Only supported for `KeyboardEvent` and `MouseEvent`, not all `UIEvent` objects.	15 ≤12.1-15 Only supported for `KeyboardEvent` and `MouseEvent`, not all `UIEvent` objects.	≤4	≤37	18	4 On `mousemove` events, the `which` property is incorrectly always set to `1`.	14 ≤12.1-14 Only supported for `KeyboardEvent` and `MouseEvent`, not all `UIEvent` objects.	≤3	1.0