原生js获取css中class的方法

function getByClass( className, context) {
    var context = context || document;
    if( context.getElementsByClassName) {
        return context.getElementsByClassName(className);
    }
    var nodes = context.getElementsByTagName("*");
    ret=[];
    for( var i=0; i<nodes.length; i++) {
        if( hasClass(nodes[i],className)) {
            ret.push(nodes[i]);
        }
    }
    return ret;
}
function hasClass ( node, className) {
    var names = node.className.split(/\s+/);
    for ( var i=0;i<names.length;i++) {
        if(names[i]==className) {
            return true;
        }
    }
    return false;
}