When the page is very long, users want to go back to the top of the page, you must scroll several times to scroll to the top, if the lower right corner of the page has a "back to the Top" button, the user clicks, you can go back to the top, for users, is a better experience.
Implementation principle: When the page loads, the element is positioned to the lower right corner of the page, when the page scrolling, the element is always in the lower right corner, when the user clicks, the page back to the top.
Point one: Document.documentElement.clientWidth | | Document.body.clientWidth; Gets the width of the viewable area. The back is compatible with chrome, and the front is compatible with other browsers.
Point two: OTop.style.left = screenw-otop.offsetwidth + "px"; When the page loads, the position of the element is at the far right of the page, minus the width of the element itself with the width of the visual area.
Point three: OTop.style.top = screenh-otop.offsetheight + scrolltop + "px"; When the page scrolls, the y-coordinate position of the element equals the height of the viewable area minus the height of the element itself, plus the scrolling distance.
Point four: document.documentElement.scrollTop = Document.body.scrollTop = 0; When clicking on an element, let the page scroll 0. Write two to be compatible.
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