javascript实现document.getElementByClass的方法

function getElementsByClassName (className) {
var all = document.all ? document.all : document.getElementsByTagName( ' *' );
var elements = new Array();
for ( var e = 0; e < all.length; e ++ ) {
if (all[e].className == className) {
elements[elements.length] = all[e];
}
}
return elements;
}