UIEvent: which property

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.

Value

Value for KeyboardEvent

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 charCode and keyCode for more details.

[!NOTE] Consider key or code for new code.

Value for MouseEvent

For MouseEvent, event.which is 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 button for new code.

Examples

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

function showKeyPress(evt) {
  console.log(
    `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) {
  console.log(
    `onkeydown handler:\n` +
      `keyCode property: ${evt.keyCode}\n` +
      `which property: ${evt.which}\n`,
  );
}

document.addEventListener("keypress", showKeyPress);
document.addEventListener("keydown", keyDown);

Specifications

Browser compatibility

See also

• KeyboardEvent
• MouseEvent