MouseEvent.button

The MouseEvent.button read-only property indicates which button was pressed on the mouse to trigger the event.

This property only guarantees to indicate which buttons are pressed during events caused by pressing or releasing one or multiple buttons. As such, it is not reliable for events such as mouseenter, mouseleave, mouseover, mouseout or mousemove.

Users may change the configuration of buttons on their pointing device so that if an event's button property is zero, it may not have been caused by the button that is physically left–most on the pointing device; however, it should behave as if the left button was clicked in the standard button layout.

Syntax

var buttonPressed = instanceOfMouseEvent.button

Return value

A number representing a given button:

• 0: Main button pressed, usually the left button or the un-initialized state
• 1: Auxiliary button pressed, usually the wheel button or the middle button (if present)
• 2: Secondary button pressed, usually the right button
• 3: Fourth button, typically the Browser Back button
• 4: Fifth button, typically the Browser Forward 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.

Example

<script>
var whichButton = function (e) {
    // Handle different event models
    var e = e || window.event;
    var btnCode;

    if ('object' === typeof e) {
        btnCode = e.button;

        switch (btnCode) {
            case 0:
                console.log('Left button clicked.');
            break;

            case 1:
                console.log('Middle button clicked.');
            break;

            case 2:
                console.log('Right button clicked.');
            break;

            default:
                console.log('Unexpected code: ' + btnCode);
        }
    }
}
</script>

<button onmouseup="whichButton(event);" oncontextmenu="event.preventDefault();">Click with mouse...</button>

Specifications

Specification	Status	Comment
Document Object Model (DOM) Level 3 Events Specification The definition of 'MouseEvent.button' in that specification.	Working Draft	Compared to Document Object Model (DOM) Level 2 Events Specification, the return value can be negative.
Document Object Model (DOM) Level 2 Events Specification The definition of 'MouseEvent.button' in that specification.	Recommendation	Initial definition.

Browser compatibility

[1] This convention is not followed in Internet Explorer prior to version 9: see QuirksMode for details.

See also

• "MouseEvent"