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The append() method of the FormData interface appends a new value onto an existing key inside a FormData object, or adds the key if it does not already exist.
The difference between FormData.set and append() is that if the specified key already exists, FormData.set will overwrite all existing values with the new one, whereas append() will append the new value onto the end of the existing set of values.
Note: This method is available in Web Workers.
语法
There are two versions of this method: a two and a three parameter version:
formData.append(name, value); formData.append(name, value, filename);
参数
name- The name of the field whose data is contained in
value. value- The field's value. This can be a
USVStringorBlob(including subclasses such asFile). filename可选- The filename reported to the server (a
USVString), when aBloborFileis passed as the second parameter. The default filename forBlobobjects is "blob". The default filename forFileobjects is the file's filename.
注意： If you specify a Blob as the data to append to the FormData object, the filename that will be reported to the server in the "Content-Disposition" header used to vary from browser to browser.
返回值
空
示例
下面的代码创建了一个空的 FormData 对象：
var formData = new FormData(); // Currently empty
你可以通过 FormData.append 往对象里加入键值对：
formData.append('username', 'Chris');
formData.append('userpic', myFileInput.files[0], 'chris.jpg');
As with regular form data, you can append multiple values with the same name. For example (and being compatible with PHP's naming conventions by adding [] to the name):
formData.append('userpic[]', myFileInput1.files[0], 'chris1.jpg');
formData.append('userpic[]', myFileInput2.files[0], 'chris2.jpg');
This technique makes it simpler to process multi-file uploads because the resultant data structure is more conducive to looping.
规范
| Specification | Status | Comment |
|---|---|---|
| XMLHttpRequest append() |
Living Standard | Initial definition |
浏览器兼容性
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | 7 | 4.0 (2.0)[1] | 10 | 12 | 5 |
| append with filename | (Yes) | 22.0 (22.0) | ? | ? | ? |
| Available in web workers | (Yes) | 39.0 (39.0) | ? | ? | ? |
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | Firefox OS (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|---|
| Basic support | 3.0[2] | ? | 4.0 (2.0)[1] | 1.0.1 | ? |
12 |
? |
| append with filename | ? | ? | 22.0 (22.0) | 1.2 | ? | ? | ? |
| Available in web workers | ? | ? | 39.0 (39.0) | ? | ? | ? | ? |
[1] Prior to Gecko 7.0 (Firefox 7.0 / Thunderbird 7.0 / SeaMonkey 2.4), if you specified a Blob as the data to append to the object, the filename reported in the "Content-Disposition" HTTP header was an empty string; this resulted in errors being reported by some servers. Starting in Gecko 7.0 the filename "blob" is sent.
[2] XHR in Android 4.0 sends empty content for FormData with blob.