Serializing form function

serializeForm.js

function serialize(form) {
    var parts = [],
        field = null,
        i,
        len,
        j,
        optLen,
        option,
        optValue;
        
    for (i = 0, len = form.elements.length; i < len, i++) {
        field = form.elements[i];
        
        switch(field.type) {
            case "select-one":
            case "select-multiple":
                
                if (field.name.length) {
                    for ( j = 0, optLen = field.options.length; j < optLen; j++) {
                        option = field.options[j];
                        if (option.selected) {
                            optValue = "";
                            if (option.hasAttribute) { //DOM compliant browsers
                                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":  //custon button
                break;
                
            case "radio":    //radio button
            case "checkbox": //checkbox
                if (!field.name) {
                    break;
                }
                /* falls through */
                
            default: 
                //don't include form fields without names
                if (field.name.length) {
                    parts.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(field.value));
                }
        }
    }
    return parts.join("&");
}