What are the difference between the scrollX and pageXOffset

Question

Are the following methods same?

window.scrollX  === window.pageXOffset

window.scrollY  === window.pageYOffset

If there is no difference, why two methods are introduced?

Answer 1

From MDN:

The pageXOffset property is an alias for the scrollX property:

window.pageXOffset == window.scrollX; // always true 

For cross-browser compatibility, use window.pageXOffset instead of window.scrollX. Additionally, older versions of Internet Explorer (< 9) do not support either property and must be worked around by checking other non-standard properties.

Same thing goes for scrollY and pageYOffset.

Source: https://developer.mozilla.org/en-US/docs/Web/API/Window.scrollX