is an alias for
scrollY; as such, it returns the number
of pixels the document is currently scrolled along the vertical axis (that is, up or
down) with a value of 0.0, indicating that the top edge of the
is currently aligned with the top edge of the window's content area.
There is slightly better support for
pageYOffset than for
scrollY in older browsers, but if you're not concerned about browsers more
than a handful of years old, you can use either one.
yOffset = window.pageYOffset;
A floating-point number specifying the number of pixels the
scrolled vertically within its containing
Window. This number is subpixel
precise, so it may not be an integer. A value of 0.0 indicates that the window is not
scrolled vertically, and that the top of the document is located at the top edge of the
window's content area.
Since this property is an alias for
Window.scrollY, see that article for
additional details on this value and its use.
In this example, an
<iframe> is created and filled with content, then
a specific element within the document is scrolled into view in the frame. Once that's
done, the vertical scroll position is checked by looking at the value of
pageYOffset in the frame's
The HTML is extremely simple and has just two elements: an
that contains the document we're going to scroll, and a
which we'll output the value of
pageYOffset when we've finished the scroll.
<iframe id="frame"> </iframe> <div id="info"> </div>
var frame = document.getElementById("frame"); var frameDoc = frame.contentDocument; var info = document.getElementById("info"); var target = frameDoc.getElementById("overview"); frameDoc.scrollingElement.scrollTop = target.offsetTop; info.innerText = "Y offset after scrolling: " + frame.contentWindow.pageYOffset + " pixels";
<iframe> element that contains our content as well as the
<div> element into which we'll output the result of our scroll
position check. It then gets a reference to the element we want to scroll into view
getElementById() on the frame's
With the target element in hand, we set the
scrollTop of the frame's
scrollingElement to the
offsetTop of the target
element. By doing so, we set the vertical scrolling position of the frame's document so
that it's the same as the top edge of the target element.
This will automatically set the scrolling position to the maximum possible value if the attempted scroll would exceed the maximum. This prevents us from falling off the edge of the document. Nobody wants to know what's out there. There might be dragons.
The result follows. Note that the frame's contents have been scrolled to show the
section named "Overview", and that the value of the
pageYOffset property is
shown with the corresponding value.
|CSS Object Model (CSSOM) View Module
The definition of 'window.pageYOffset' in that specification.
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