Document.body.scrollTop a quick solution to the total zero value _javascript tips

There is a function to determine whether the return Top button is displayed.

The JS code is as follows:

var sTop = Document.body.scrollTop;
  if (stop>100) {
    document.getElementById ("Sm_top"). style.display= "Block";
  else{
    document.getElementById ("Sm_top"). style.display= "None";
  

But Document.body.scrollTop has been found to be 0.

The discovery of data is a DTD problem.

The page specifies a DTD, that is, when DOCTYPE is specified, the document.documentelement is used.

The page does not have a DTD, that is, when DOCTYPE is not specified, use Document.body.

This is true for both IE and Firefox.

And my page adds <!. DOCTYPE Html>, so you can.

 /* Judge back to the top button display or not * *
   window.onscroll=function () {
    var sTop = Document.documentElement.scrollTop;
  if (stop>100) {
    document.getElementById ("Sm_top"). style.display= "Block";
  else{
    document.getElementById ("Sm_top"). style.display= "None";
  }
  

The above is a small set of Document.body.scrollTop to introduce the value of total zero for the solution, I hope to help you!