offsetX

Gets the distance in pixels between the pointer and the left edge of the element that triggered this event.

Scrolling the web page causes its elements to shift relative to the browser window. Therefore, two clicks on the same physical point of the screen return different offsetX values if the page is scrolled horizontally in the meantime. But two clicks on the same point on the element return the same offsetX values even if the page is scrolled horizontally in the meantime.