document.getElementsByClass = function(className){
    
    var eles, count;
    
    if(typeof this.all === 'undefined'){
        eles = this.getElementsByTagName('*');
        count = eles.length;
    }else{
        count = this.all.length;
        eles = this.all;
    }

    var _nodes = {
        count : count,
        eles : eles
    },
    pattern = new RegExp(className, 'g'),
    results = [];
    
    for(var i = 0; i < _nodes.count; i += 1){
        
        var classes = _nodes.eles[i].className;
        
        if( typeof classes !== 'undefined'){
            if(pattern.test(classes)){
                results.push(_nodes.eles[i]);
            }
        }
        
    }
    
    if(results.length === 0){
        results = undefined;
    }
    
    return results;

}