There are several questions on StackOverflow regarding offsetWidth/clientWidth/scrollWidth (and -Height, respectively), but none give comprehensive explanation of what those values are.
Also, there are several sources on the web giving confusing or incorrect information.
Can you give a complete explanation including some visual hints?
Also, how can those values be used to calculate scroll bar widths?
The CSS box model is rather complicated, particularly when it comes to scrolling content. While the browser uses the values from your CSS to draw boxes, determining all the dimensions using JS is not straight-forward if you only have the CSS.
That's why each element has six DOM properties for your convenience:
scrollHeight. These are read-only attributes representing the current visual layout, and all of them are integers (thus possibly subject to rounding errors).
Let's go through them in detail:
offsetHeight: The size of the visual box incuding all borders. Can be calculated by adding
heightand paddings and borders, if the element has
clientHeight: The visual portion of the box content, not including borders or scroll bars , but includes padding . Can not be calculated directly from CSS, depends on the system's scroll bar size.
scrollHeight: The size of all of the box's content, including the parts that are currently hidden outside the scrolling area. Can not be calculated directly from CSS, depends on the content.
clientWidth takes the scroll bar width into account, we can use it to calculate the scroll bar width via the formula
scrollbarWidth = offsetWidth - clientWidth - getComputedStyle().borderLeftWidth - getComputedStyle().borderRightWidth
Unfortunately, we may get rounding errors, since
clientWidth are always integers, while the actual sizes may be fractional with zoom levels other than 1.
Note that this
scrollbarWidth = getComputedStyle().width + getComputedStyle().paddingLeft + getComputedStyle().paddingRight - clientWidth
does not work reliably in Chrome, since Chrome returns
width with scrollbar already substracted. (Also, Chrome renders paddingBottom to the bottom of the scroll content, while other browsers don't)