MouseEvent: movementX property

{{APIRef("Pointer Lock API")}}

The movementX read-only property of the {{domxref("MouseEvent")}} interface provides the difference in the X coordinate of the mouse (or pointer) between the given move event and the previous move event of the same type.

In other words, the value of the property is computed like this: currentEvent.movementX = currentEvent.screenX - previousEvent.screenX. The value is zero for all events other than {{domxref("Element/mousemove_event", "mousemove")}}, {{domxref("Element/pointermove_event", "pointermove")}}, and {{domxref("Element/pointerrawupdate_event", "pointerrawupdate")}}.

[!WARNING] Browsers use different units for movementX and screenX than what the specification defines. Depending on the browser and operating system, the movementX units may be a physical pixel, a logical pixel, or a CSS pixel. You may want to avoid the movement properties, and instead calculate the delta between the current client values ({{domxref("MouseEvent.screenX", "screenX")}}, {{domxref("MouseEvent.screenY", "screenY")}}) and the previous client values.

Value

A number. Always zero on any {{domxref("MouseEvent")}} other than mousemove, and any {{domxref("PointerEvent")}} other than pointermove or pointerrawupdate.

Examples

Log mouse movement for mousemove events

This example logs the amount of mouse movement using movementX and {{domxref("MouseEvent.movementY", "movementY")}}.

HTML

<p id="log">Move your mouse around.</p>

JavaScript

const log = document.getElementById("log");

function logMovement(event) {
  log.insertAdjacentHTML(
    "afterbegin",
    `movement: ${event.movementX}, ${event.movementY}
`,
  );
  while (log.childNodes.length > 128) log.lastChild.remove();
}

document.addEventListener("mousemove", logMovement);

Result

{{EmbedLiveSample("### Log mouse movement for mousemove events")}}

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{domxref("MouseEvent.movementY")}}
• {{domxref("MouseEvent")}}
• Pointer Lock