JavaScript: AjaxForm

ajax_form.js

/**
 * Overrides the browser's form submission and sends the form via ajax instead.
 * Uses the microajax function: https://code.google.com/p/microajax/
 */

var AjaxForm = {
    iframe: null,
    form: null,
    submit: function(form) {
        if(PageChangeWarning) {
            PageChangeWarning.saved();
        }
        this.form = form;
        var has_file = false;
        var inputs = form.getElementsByTagName('input');
        for (var i = 0, n = inputs.length; i < n; i++)
        {
            if (inputs[i].getAttribute('type') == 'file')
            {
                has_file = true;
            }
        }
        if(has_file) {
            this.submit_with_file(form);
        } else {
            this.submit_with_ajax(form);
        }
    },
    submit_with_ajax: function(form) {
        var url = form.getAttribute('action');
        var data = AjaxForm.serialize(form);
        form.classList.add('hidden');
        microAjax(url, this.form_response.bind(this), data);
    },
    submit_with_file: function(form) {
        var id = 'iframe_' + Math.random();
        var iframe = document.createElement('iframe');
        iframe.setAttribute('name',id);
        iframe.setAttribute('style','display: none');
        document.body.appendChild(iframe);
        form.setAttribute('method','post');
        form.setAttribute('enctype','multipart/form-data');
        form.setAttribute('target',id);
        this.iframe = iframe;
        iframe.addEventListener('load',this.form_response.bind(this));
        this.form.submit();
    },
    form_response: function(json) {
        if(this.iframe) {
            var content = this.iframe.contentWindow.document.body.innerHTML;
            // Strip anything that's not JSON
            var json_matches = content.match(/[^{]*([^}]*})/);
            if (json_matches[0]) {
                json = json_matches[1];
            }
            document.body.removeChild(this.iframe);
            this.iframe = null;
        }
        if(json) {
            if(JsonProcessor.run(json)) {
                this.form.classList.remove('hidden');
            }
        }
    },
    submit_button_click: function(form_id) {
        var form = document.getElementById(form_id);
        this.submit(form);
    },

    serialize: function(form) {
        if (!form || !form.elements)
            return;

        var serial = [], i, j, first;
        var add = function (name, value) {
            serial.push(encodeURIComponent(name) + '=' + encodeURIComponent(value));
        };

        var elems = form.elements;
        for (i = 0; i < elems.length; i += 1, first = false) {
            if (elems[i].name.length > 0) { /* don't include unnamed elements */
                switch (elems[i].type) {
                    case 'select-one':
                        first = true;
                    case 'select-multiple':
                        for (j = 0; j < elems[i].options.length; j += 1)
                            if (elems[i].options[j].selected) {
                                add(elems[i].name, elems[i].options[j].value);
                                if (first)
                                    break; /* stop searching for select-one */
                            }
                        break;
                    case 'checkbox':
                    case 'radio':
                        if (!elems[i].checked)
                            break; /* else continue */
                    default:
                        add(elems[i].name, elems[i].value);
                        break;
                }
            }
        }

        return serial.join('&');
    }
};