How to Resolve the \'multipart boundary\' Error in XMLHttpRequest File Uploads?

Troubleshooting XMLHttpRequest File Uploads

File uploads with XMLHttpRequest can sometimes encounter errors, especially when dealing with multipart data. Here's a detailed analysis of a common issue involving the "multipart boundary" error.

The provided code attempts to upload a file using XMLHttpRequest, but it fails with the following error:

The request was rejected because no multipart boundary was found.

Incorrect File Attachment

The initial code includes the line xhr.file = file;. However, this is not a standard way to attach a file to an XMLHttpRequest. The file object should be wrapped inside a FormData object.

Form Data Usage

To resolve this issue, replace xhr.send(file); with the following code:

var formData = new FormData();
formData.append("thefile", file);
xhr.send(formData);

Multipart/Form-Data Header

Ensure that the Content-Type header is set to "multipart/form-data" before sending the request:

xhr.setRequestHeader("Content-Type", "multipart/form-data");

Additional Notes

• The FormData object creates a multipart/form-data request object that can be parsed on the server using PHP's $_FILES['thefile'].
• For more information on XMLHttpRequest file uploads, refer to Mozilla Hack demos and MDC documentation.

By following these steps and correcting the code errors, you can successfully upload files using XMLHttpRequest.

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