Javscript form serialize

function serialize(form){        
    var parts = new Array();
    var field = null;
 
    for (var i=0, len=form.elements.length; i < len; i++){
        field = form.elements[i];
 
        switch(field.type){
            case "select-one":
            case "select-multiple":
                for (var j=0, optLen = field.options.length; j < optLen; j++){
                var option = field.options[j];
                if (option.selected){
                    var optValue = "";
                    if (option.hasAttribute){
                        optValue = (option.hasAttribute("value") ? option.value : option.text);
                    } else {
                        optValue = (option.attributes["value"].specified ? option.value : option.text);
                    }
                    parts.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(optValue));
                }
            }
            break;
    
            case undefined:     //fieldset
            case "file":        //file input
            case "submit":      //submit button
            case "reset":       //reset button
            case "button":      //custom button
            break;
    
            case "radio":       //radio button
            case "checkbox":    //checkbox
                if (!field.checked){
                    break;
                }
                /* falls through */
       
            default:
                parts.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(field.value));
        }
    }        
    return parts.join("&");
}