We're looking for a user researcher to understand the needs of developers and designers. Is this you or someone you know? Check out the post: https://mzl.la/2IGzdXS


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 MouseEvent.which read-only property indicates which button was pressed on the mouse to trigger the event. The standard alternatives to this property are MouseEvent.button and MouseEvent.buttons.


var buttonPressed = instanceOfMouseEvent.which

Return value

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.


This is not part of any specification.

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

Feature Edge Firefox (Gecko) Chrome Internet Explorer Opera Safari
Basic support (Yes) 1.0 (1.7 or earlier)[1] 1.0 9.0 5.0 1.0
Feature Edge Firefox Mobile (Gecko) Android IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) 1.0 (1) [1] (Yes) (Yes) (Yes) (Yes)

[1] On mousemove events, the which property is incorrectly always set to 1 bug 1048294.

See also

Document Tags and Contributors

Contributors to this page: libbymc, Ac1521, cvrebert, Sebastianz, teoli, Marijn
Last updated by: libbymc,