FormData对象

FF4中增加了一个很有意思的对象，FormData。通常我们提交（使用submit button）时，会把form中的所有表格元素的name与value组成一个queryString，提交到后台。这用jQuery的方法来说，就是serialize。但当我们使用Ajax提交时，这过程就要变成人工的了。因此，FormData对象的出现可以减少我们一些工作量。

想得到一个FormData对象，很简单：

 var formdata = new FormData();

但一个空的FormData对象对我们没有意义，因此W3c草案提供了三种方案来获取或修改FormData。

方案1：创建一个空的FormData对象，然后再用append方法逐个添加键值对：

var formdata = new FormData();
formdata.append("name", "司徒正美"); 
formdata.append("blog", "http://www.cnblogs.com/rubylouvre/");

方案2：取得form元素对象，将它作为参数传入FormData对象中！

        var formobj =  document.getElementById("form");
        var formdata = new FormData(formobj);

方案3：利用form元素对象的getFormData方法生成它！

        var formobj =  document.getElementById("form");
        var formdata = formobj.getFormData()

注意，formdata是一个不透明的对象，现在暂时只有一个append可以操作，不能通过序列化手段得到其里面的内容，这实在是遗憾。它的用法现在也只有一个，用于增强型的XMLHttpRequest对象的send方法中去！

 var formElement = document.getElementById("myFormElement");
formData = formElement.getFormData();
formData.append("serialnumber", serialNumber++);
xhr.send(formData);

相关链接：Firefox 4: easier JS form handling with FormData

https://gist.github.com/3120320

/* * FormData for XMLHttpRequest 2 - Polyfill for Web Worker (c) 2012 Rob W * License: Creative Commons BY - http://creativecommons.org/licenses/by/3.0/ * - append(name, value[, filename]) * - toString: Returns an ArrayBuffer object * * Specification: http://www.w3.org/TR/XMLHttpRequest/#formdata * http://www.w3.org/TR/XMLHttpRequest/#the-send-method * The .append() implementation also accepts Uint8Array and ArrayBuffer objects * Web Workers do not natively support FormData: * http://dev.w3.org/html5/workers/#apis-available-to-workers **/ (function() { // Export variable to the global scope (this == undefined ? self : this)['FormData'] = FormData; var ___send$rw = XMLHttpRequest.prototype.send; XMLHttpRequest.prototype['send'] = function(data) { if (data instanceof FormData) { if (!data.__endedMultipart) data.__append('--' + data.boundary + '--\r\n'); data.__endedMultipart = true; this.setRequestHeader('Content-Type', 'multipart/form-data; boundary=' + data.boundary); data = new Uint8Array(data.data).buffer; } // Invoke original XHR.send return ___send$rw.call(this, data); }; function FormData() { // Force a Constructor if (!(this instanceof FormData)) return new FormData(); // Generate a random boundary - This must be unique with respect to the form's contents. this.boundary = '------WebKitFormBoundary' + Math.random().toString(36); var internal_data = this.data = []; /** * Internal method. * @param inp String | ArrayBuffer | Uint8Array Input */ this.__append = function(inp) { var i=0, len; if (typeof inp === 'string') { for (len=inp.length; i<len; i++) internal_data.push(inp.charCodeAt(i) & 0xff); } else if (inp && inp.byteLength) {/*If ArrayBuffer or typed array */ if (!('byteOffset' in inp)) /* If ArrayBuffer, wrap in view */ inp = new Uint8Array(inp); for (len=inp.byteLength; i<len; i++) internal_data.push(inp[i] & 0xff); } }; } /** * @param name String Key name * @param value String|Blob|File|Uint8Array|ArrayBuffer Value * @param filename String Optional File name (when value is not a string). **/ FormData.prototype['append'] = function(name, value, filename) { if (this.__endedMultipart) { // Truncate the closing boundary this.data.length -= this.boundary.length + 6; this.__endedMultipart = false; } var valueType = Object.prototype.toString.call(value), part = '--' + this.boundary + '\r\n' + 'Content-Disposition: form-data; name="' + name + '"'; if (/^\[object (?:Blob|File)(?:Constructor)?\]$/.test(valueType)) { return this.append(name, new Uint8Array(new FileReaderSync().readAsArrayBuffer(value)), filename || value.name); } else if (/^\[object (?:Uint8Array|ArrayBuffer)(?:Constructor)?\]$/.test(valueType)) { part += '; filename="'+ (filename || 'render.png').replace(/"/g,'%22') +'"\r\n'; part += 'Content-Type: image/png\r\n\r\n'; this.__append(part); this.__append(value); part = '\r\n'; } else { part += '\r\n\r\n' + value + '\r\n'; } this.__append(part); }; })();