FormData: append() method
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
Note: This feature is available in Web Workers.
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 set() and append() is that if the specified key already exists, 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.
Syntax
append(name, value)
append(name, value, filename)
Parameters
name-
The name of the field whose data is contained in
value. value-
The field's value. This can be a string or
Blob(including subclasses such asFile). If none of these are specified the value is converted to a string. filenameOptional-
The filename reported to the server (a string), when a
BloborFileis passed as the second parameter. The default filename forBlobobjects is "blob". The default filename forFileobjects is the file's filename.
Note:
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.
Return value
None (undefined).
Examples
formData.append("username", "Chris");
When the value is a Blob (or a File), you can specify its name with the filename parameter:
formData.append("user-pic", myFileInput.files[0], "chris.jpg");
As with regular form data, you can append multiple values with the same name:
formData.append("user-pic", myFileInput.files[0], "chris1.jpg");
formData.append("user-pic", myFileInput.files[1], "chris2.jpg");
If the value is not a string or a Blob, append() will convert it to a string automatically:
formData.append("name", true);
formData.append("name", 72);
formData.getAll("name"); // ["true", "72"]
Specifications
| Specification |
|---|
| XMLHttpRequest # dom-formdata-append |
Browser compatibility
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