利用FormData对象,你可以使用一系列的键值对来模拟一个完整的表单,然后使用XMLHttpRequest发送这个”表单”.

创建一个FormData对象

var oMyForm = new FormData();

oMyForm.append("username", "Groucho");
oMyForm.append("accountnum", 123456); // 数字123456被立即转换成字符串"123456"

// fileInputElement中已经包含了用户所选择的文件
oMyForm.append("userfile", fileInputElement.files[0]);

var oFileBody = "<a id="a"><b id="b">hey!</b></a>"; // Blob对象包含的文件内容
var oBlob = new Blob([oFileBody], { type: "text/xml"});

oMyForm.append("webmasterfile", oBlob);

var oReq = new XMLHttpRequest();
oReq.open("POST", "submitform.php");
oReq.send(oMyForm);

使用HTML表单来初始化一个FormData对象

var formElement = document.getElementById("myFormElement");
var oReq = new XMLHttpRequest();
oReq.open("POST", "submitform.php");
oReq.send(new FormData(formElement));

还可以在已有表单数据的基础上,继续添加新的键值对,如下:

var formElement = document.getElementById("myFormElement");
formData = new FormData(formElement);
formData.append("serialnumber", serialNumber++);
oReq.send(formData);

使用FormData对象发送文件

<form enctype="multipart/form-data" method="post" name="fileinfo">
  <label>Your email address:</label>
  <input type="email" autocomplete="on" autofocus name="userid" placeholder="email" required size="32" maxlength="64" />
</form>
<div id="output"></div>
<a href="javascript:sendForm()">Stash the file!</a>

使用下面的代码来异步的上传用户所选择的文件:

function sendForm() {
  var oOutput = document.getElementById("output");
  var oData = new FormData(document.forms.namedItem("fileinfo"));

  oData.append("CustomField", "This is some extra data");

  var oReq = new XMLHttpRequest();
  oReq.open("POST", "stash.php", true);
  oReq.onload = function(oEvent) {
    if (oReq.status == 200) {
      oOutput.innerHTML = "Uploaded!";
    } else {
      oOutput.innerHTML = "Error " + oReq.status + " occurred uploading your file.<br \/>";
    }
  };

  oReq.send(oData);
}

如果FormData对象中的某个字段值是一个Blob对象,则在发送http请求时,代表该Blob对象所包含文件的文件名的”Content-Disposition”请求头的值在不同的浏览器下有所不同,Firefox使用了固定的字符串”blob,”而Chrome使用了一个随机字符串.

使用jQuery来发送FormData

你还可以使用jQuery来发送FormData,但必须要正确的设置相关选项:

var fd = new FormData(document.getElementById("fileinfo"));
fd.append("CustomField", "This is some extra data");
$.ajax({
  url: "stash.php",
  type: "POST",
  data: fd,
  processData: false,  // 告诉jQuery不要去处理发送的数据
  contentType: false   // 告诉jQuery不要去设置Content-Type请求头
}); 
        

上传文件显示进度

          function fileSelected() {
            var file = document.getElementById('fileToUpload').files[0];
            if (file) {
                var fileSize = 0;
                if (file.size > 1024 * 1024)
                    fileSize = (Math.round(file.size * 100 / (1024 * 1024)) / 100).toString() + 'MB';
                else
                    fileSize = (Math.round(file.size * 100 / 1024) / 100).toString() + 'KB';

                document.getElementById('fileName').innerHTML = 'Name: ' + file.name;
                document.getElementById('fileSize').innerHTML = 'Size: ' + fileSize;
                document.getElementById('fileType').innerHTML = 'Type: ' + file.type;

            }

        }
            function uploadFile() {
            var fd = new FormData();
fd.append("fileToUpload",document.getElementById('fileToUpload').files[0]);
            var xhr = new XMLHttpRequest();
            xhr.upload.addEventListener("progress", uploadProgress, false);
            xhr.addEventListener("load", uploadComplete, false);
            xhr.addEventListener("error", uploadFailed, false);
            xhr.addEventListener("abort", uploadCanceled, false);
            xhr.open("POST", "Home/Upload");
            xhr.send(fd);
        }
    function uploadProgress(evt) {
            if (evt.lengthComputable) {
                var nowDate = new Date().getTime();
                taking = nowDate - startDate;
                var x = (evt.loaded) / 1024;
                var y = taking / 1000;
                var uploadSpeed = (x / y);
                var formatSpeed;
                if (uploadSpeed > 1024) {
                    formatSpeed = (uploadSpeed / 1024).toFixed(2) + "Mb\/s";
                } else {
                    formatSpeed = uploadSpeed.toFixed(2) + "Kb\/s";
                }
                var percentComplete = Math.round(evt.loaded * 100 / evt.total);
                progressbar.progressbar("value", percentComplete);
                // console && console.log(percentComplete, ",", formatSpeed);
            }
    }
            function uploadComplete(evt) {
            /* This event is raised when the server send back a response */
            alert(evt.target.responseText);

        }
        function uploadFailed(evt) {
            alert("There was an error attempting to upload the file.");
        }
        function uploadCanceled(evt) {
            alert("The upload has been canceled by the user or the browser dropped the connection.");

        }