MouseEvent.clientY

The clientY read-only property of the MouseEvent interface provides the vertical coordinate within the application's viewport at which the event occurred (as opposed to the coordinate within the page).

For example, clicking on the top edge of the viewport will always result in a mouse event with a clientY value of 0, regardless of whether the page is scrolled vertically.

var y = instanceOfMouseEvent.clientY

A double floating point value, as redefined by the CSSOM View Module. Originally, this property was defined as a long integer. See the "Browser compatibility" section for details.

This example displays your mouse's coordinates whenever you trigger the mousemove event.

<p>Move your mouse to see its position.</p>
<p id="screen-log"></p>

let screenLog = document.querySelector('#screen-log');
document.addEventListener('mousemove', logKey);

function logKey(e) {
  screenLog.innerText = `
    Screen X/Y: ${e.screenX}, ${e.screenY}
    Client X/Y: ${e.clientX}, ${e.clientY}`;
}

• MouseEvent
• clientX
• screenX / screenY