UIEvent: which property

{{APIRef("UI Events")}}{{Deprecated_Header}}

The UIEvent.which read-only property of the {{domxref("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 {{Non-standard_Inline}}

For {{domxref("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 {{domxref("KeyboardEvent.charCode")}} and {{domxref("KeyboardEvent.keyCode")}} for more details.

[!NOTE] Consider {{domxref("KeyboardEvent.key")}} or {{domxref("KeyboardEvent.code")}} for new code.

Value for MouseEvent {{Non-standard_Inline}}

For {{domxref("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 {{domxref("MouseEvent.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

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{domxref("KeyboardEvent")}}
• {{domxref("MouseEvent")}}