MouseEvent: movementX property

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The movementX read-only property of the MouseEvent interface provides the difference in the X coordinate of the mouse pointer between the given event and the previous mousemove event. In other words, the value of the property is computed like this: currentEvent.movementX = currentEvent.screenX - previousEvent.screenX.

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 (screenX, screenY) and the previous client values.

<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}<br>`,
  );
  while (log.childNodes.length > 128) log.lastChild.remove();
}

document.addEventListener("mousemove", logMovement);