How to Resolve the Multipart Boundary Error in File Uploads Using Ajax XMLHttpRequest?

File Upload Utilizing Ajax XMLHttpRequest: Resolving Multipart Boundary Error

In an attempt to transfer a file using XMLHttpRequest, you might encounter the following error:

The request was rejected because no multipart boundary was found.

This error signifies that your code lacks the correct approach to handling multipart form data. To rectify this issue, let's address two key areas:

1. XHR file property: The line xhr.file = file; is superfluous. The file object should not be assigned in this manner.
2. File Transmission: Modifying xhr.send(file); won't transfer the file effectively. Instead, use the FormData object to construct the multipart/form-data payload:

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

By utilizing FormData, the file becomes accessible through the PHP variable $_FILES['thefile'].

Remember to consult documentation and demos from MDC and Mozilla Hack for further guidance on this topic.

Previous Incorrect Suggestion:

The earlier answer incorrectly stated that xhr.send(file); transmits the raw post data. While it does send the file, it's imperative to employ FormData to ensure proper parsing on the server. Therefore, the above correction is crucial for achieving the desired functionality.

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