MouseEvent: buttons property

The MouseEvent.buttons read-only property indicates which buttons are pressed on the mouse (or other input device) when a mouse event is triggered.

Each button that can be pressed is represented by a given number (see below). If more than one button is pressed, the button values are added together to produce a new number. For example, if the secondary (2) and auxiliary (4) buttons are pressed simultaneously, the value is 6 (i.e., 2 + 4).

Note: Do not confuse this property with the MouseEvent.button property. The MouseEvent.buttons property indicates the state of buttons pressed during any kind of mouse event, while the MouseEvent.button property only guarantees the correct value for mouse events caused by pressing or releasing one or multiple buttons.

Value

A number representing one or more buttons. For more than one button pressed simultaneously, the values are combined (e.g., 3 is primary + secondary).

0: No button or un-initialized
1: Primary button (usually the left button)
2: Secondary button (usually the right button)
4: Auxiliary button (usually the mouse wheel button or middle button)
8: 4th button (typically the "Browser Back" button)
16 : 5th button (typically the "Browser Forward" button)

Examples

This example logs the buttons property when you trigger a mousedown event.

HTML

html

<p>Click anywhere with one or more mouse buttons.</p>
<pre id="log">[No clicks yet]</pre>

JavaScript

const buttonNames = ["left", "right", "wheel", "back", "forward"];
function mouseButtonPressed(event, buttonName) {
  // Use binary `&` with the relevant power of 2 to check if a given button is pressed
  return Boolean(event.buttons & (1 << buttonNames.indexOf(buttonName)));
}

function format(event) {
  const { type, buttons } = event;
  const obj = { type, buttons };
  for (const buttonName of buttonNames) {
    obj[buttonName] = mouseButtonPressed(event, buttonName);
  }
  return JSON.stringify(obj, null, 2);
}

const log = document.getElementById("log");
function logButtons(event) {
  log.textContent = format(event);
}

document.addEventListener("mouseup", logButtons);
document.addEventListener("mousedown", logButtons);

Result

Specifications

Pointer Events

Firefox notes

Firefox supports the buttons attribute on Windows, Linux (GTK), and macOS with the following restrictions:

Utilities allow customization of button actions. Therefore, primary might not be the left button on the device, secondary might not be the right button, and so on. Moreover, the middle (wheel) button, 4th button, and 5th button might not be assigned a value, even when they are pressed.
Single-button devices may emulate additional buttons with combinations of button and keyboard presses.
Touch devices may emulate buttons with configurable gestures (e.g., one-finger touch for primary, two-finger touch for secondary, etc.).
On Linux (GTK), the 4th button and the 5th button are not supported. In addition, a mouseup event always includes the releasing button information in the buttons value.
On Mac OS X 10.5, the buttons attribute always returns 0 because there is no platform API for implementing this feature.