------希望大家指正错误，深表感谢
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<div class="ss" id="demo"></div>
<span class="ss"></span>
<div class="sss"></div>
<script>
window.onload = function(){
function getClass(classStr){
if(document.getElementsByClassName){
return document.getElementsByClassName(classStr);
}else{
var nodes = document.getElementsByTagName('*');
var results = [];
for(var i = 0;i<nodes.length;i++){
if(hasClassName(nodes[i],classStr)){
results.push(nodes[i]);
}
}
return results;
}
function hasClassName(nodeStr,classStr){
var arrClassName = nodeStr.className.split(/s+/);
for(var i = 0;i<arrClassName.length;i++){
if(arrClassName[i] == classStr){
return true;
}
}
return false;
}
}
console.log(getClass('ss'));
}
</script>
</body>
</html>