ascx页面获取标签的通用方法

function GetInput1(tagname)
    {
        var input= document.getElementsByTagName("input");
        for(var i=0;i<input.length;i++)
        {
            try{
                if(input[i].tag==tagname)
                {
                    return input[i];
                }      
            }catch(e){
                alert("不存在");
            }
          
        }
        return "";
    }
    function GetInput(tagname)
    {
        var control=GetInput1(tagname);
        if(control=="")
        {
            alert("null");
        }
        else
        {
            return control.value;
        }    
    }