serialize form in javascript

 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:
                case "file":
                case "submit":
                case "reset":
                case "button":
                    break;
                case "radio":
                case "checkbox":
                    if (!field.checked) {
                        break;
                    }
                default:
                    parts.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(optValue));
            }
        }
        return parts.join("&");
    }