The correct way to use javascript scrollTop

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 in window.pageYOffset/document.documentElement.scrollTop/document.body.scrollTop under the browser
Example:

<span style="font-size: 16px;">window.scroll(0,100)<br/>console.log(“window.pageYOffset:”+window.pageYOffset)<br/>console.log(“document.documentElement.scrollTop:”+document.documentElement.scrollTop)<br/>console.log(“document.body.scrollTop:”+document.body.scrollTop)</span>

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 the scrollTop valuePerfectly get the scrollTop value assignment abbreviation:

<span style="font-size: 16px;">var scrollTop = window.pageYOffset|| document.documentElement.scrollTop || document.body.scrollTop;</span>

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