For this type of information, we can use the root document element
document.documentElement, that corresponds to the
<html> tag. But there are additional methods and peculiarities to consider.
To get window width and height, we can use the
For instance, this button shows the height of your window:
Browsers also support properties like
window.innerWidth/innerHeight. They look like what we want, so why not to use them instead?
If there exists a scrollbar, and it occupies some space,
clientWidth/clientHeight provide the width/height without it (subtract it). In other words, they return the width/height of the visible part of the document, available for the content.
window.innerWidth/innerHeight includes the scrollbar.
If there’s a scrollbar, and it occupies some space, then these two lines show different values:
In most cases, we need the available window width in order to draw or position something within scrollbars (if there are any), so we should use
Please note: top-level geometry properties may work a little bit differently when there’s no
<!DOCTYPE HTML> in HTML. Odd things are possible.
In modern HTML we should always write
Theoretically, as the root document element is
document.documentElement, and it encloses all the content, we could measure the document’s full size as
But on that element, for the whole page, these properties do not work as intended. In Chrome/Safari/Opera, if there’s no scroll, then
documentElement.scrollHeight may be even less than
documentElement.clientHeight! Weird, right?
To reliably obtain the full document height, we should take the maximum of these properties:
let scrollHeight = Math.max( document.body.scrollHeight, document.documentElement.scrollHeight, document.body.offsetHeight, document.documentElement.offsetHeight, document.body.clientHeight, document.documentElement.clientHeight ); alert('Full document height, with scrolled out part: ' + scrollHeight);
Why so? Better don’t ask. These inconsistencies come from ancient times, not a “smart” logic.
DOM elements have their current scroll state in their
For document scroll,
document.documentElement.scrollLeft/scrollTop works in most browsers, except older WebKit-based ones, like Safari (bug 5991), where we should use
document.body instead of
Luckily, we don’t have to remember these peculiarities at all, because the scroll is available in the special properties,
These properties are read-only.
For historical reasons, both properties exist, but they are the same:
window.pageXOffsetis an alias of
window.pageYOffsetis an alias of
For instance, if we try to scroll the page with a script in
<head>, it won’t work.
Regular elements can be scrolled by changing
We can do the same for the page using
document.documentElement.scrollTop/scrollLeft (except Safari, where
document.body.scrollTop/Left should be used instead).
scrollBy(x,y)scrolls the page relative to its current position. For instance,
scrollBy(0,10)scrolls the page
The button below demonstrates this:
scrollTo(pageX,pageY)scrolls the page to absolute coordinates, so that the top-left corner of the visible part has coordinates
(pageX, pageY)relative to the document’s top-left corner. It’s like setting
To scroll to the very beginning, we can use
These methods work for all browsers the same way.
For completeness, let’s cover one more method: elem.scrollIntoView(top).
The call to
elem.scrollIntoView(top) scrolls the page to make
elem visible. It has one argument:
top=true(that’s the default), then the page will be scrolled to make
elemappear on the top of the window. The upper edge of the element will be aligned with the window top.
top=false, then the page scrolls to make
elemappear at the bottom. The bottom edge of the element will be aligned with the window bottom.
The button below scrolls the page to position itself at the window top:
And this button scrolls the page to position itself at the bottom:
Sometimes we need to make the document “unscrollable”. For instance, when we need to cover the page with a large message requiring immediate attention, and we want the visitor to interact with that message, not with the document.
To make the document unscrollable, it’s enough to set
document.body.style.overflow = "hidden". The page will “freeze” at its current scroll position.
The first button freezes the scroll, while the second one releases it.
We can use the same technique to freeze the scroll for other elements, not just for
The drawback of the method is that the scrollbar disappears. If it occupied some space, then that space is now free and the content “jumps” to fill it.
That looks a bit odd, but can be worked around if we compare
clientWidth before and after the freeze. If it increased (the scrollbar disappeared), then add
document.body in place of the scrollbar to keep the content width the same.
Width/height of the visible part of the document (content area width/height):
Width/height of the whole document, with the scrolled out part:
let scrollHeight = Math.max( document.body.scrollHeight, document.documentElement.scrollHeight, document.body.offsetHeight, document.documentElement.offsetHeight, document.body.clientHeight, document.documentElement.clientHeight );
Read the current scroll:
Change the current scroll:
window.scrollTo(pageX,pageY)– absolute coordinates,
window.scrollBy(x,y)– scroll relative the current place,
elem.scrollIntoView(top)– scroll to make
elemvisible (align with the top/bottom of the window).