js浏览器兼容问题，只有ie正常，其他浏览器都会出现问题，请高手帮我改一下，很急，在线等

这段代码除了大小写可能会有点问题，其它应该没问题
function _$(target) {
if (!document.getElementsByClassName) {
document.getElementsByClassName = function (className) {
var children = document.getElementsByTagName("*");
var elements = new Array();
for (var i = 0; i < children.length; i++) {
var child = children[i];
var classNames = child.className.split(' ');
for (var j = 0; j < classNames.length; j++) {
if (classNames[j].toUpperCase() == className.toUpperCase()) {
elements.push(child);
break;
}
}
}
return elements;
}
return document.getElementsByClassName(target);
}
else {
return document.getElementsByClassName(target);
}
}