The correct way to use javascript scrollTop_Basic knowledge

javascript scrollTop Gets the offset of the scroll bar relative to its top (such as making a "return to top" button that automatically displays and hides). In practical applications, we often encounter the following problems:
document.documentElement.scrollTop is always 0 in Chrome
document.body.scrollTop is always 0 in IE and Firefox

1, each Differences between window.pageYOffset/document.documentElement.scrollTop/document.body.scrollTop under the browser
Example:

Copy code The code is as follows:

window.scroll(0,100)
console.log(“window.pageYOffset:” window.pageYOffset)
console.log(“document.documentElement.scrollTop: ” document.documentElement.scrollTop)
console.log(“document.body.scrollTop:” document.body.scrollTop)

IE6/7/8:
doctype:
window.pageYOffset: undefined
document.documentElement.scrollTop:100
document.body.scrollTop: 0

No doctype:
window.pageYOffset: undefined
document.documentElement.scrollTop:0
document.body.scrollTop:100
Safari/Chrome:
window.pageYOffset:100
document.documentElement.scrollTop:0
document.body.scrollTop:100

Firefox/Opera:

doctype:
window.pageYOffset:100
document.documentElement.scrollTop:100
document.body.scrollTop:0

No doctype:
window.pageYOffset: 100
document.documentElement.scrollTop:0
document.body.scrollTop: 100

2. Get scrollTop value
Perfectly get scrollTop value assignment abbreviation:

Copy code The code is as follows:

var scrollTop = window.pageYOffset|| document.documentElement.scrollTop || document.body.scrollTop;