How do I Upload a Blob in JavaScript?

Uploading Blobs with JavaScript

When dealing with audio or other multimedia data in JavaScript, it's common to encounter blobs, which are immutable collections of raw data. To store or process this data effectively, you may need to upload it to a server. Here's a detailed guide on how to upload a blob using JavaScript:

Using FormData

One of the most straightforward methods of uploading a blob is through the FormData API. It's a standardized API that provides a way to create an HTTP request with a payload containing both regular form data and binary data, such as blobs.

jQuery.ajax Implementation

To upload a blob using jQuery.ajax, follow these steps:

1. Create a new FormData object:

var fd = new FormData();

2. Append both the file's name and the blob to the FormData object:

fd.append('fname', 'test.wav');
fd.append('data', soundBlob);

3. Set the processData and contentType options of the jQuery.ajax call to false:

$.ajax({
    type: 'POST',
    url: '/upload.php',
    data: fd,
    processData: false,
    contentType: false
}).done(function(data) {
       console.log(data);
});

By setting processData to false, we prevent jQuery from converting the FormData object to a string, which is necessary for binary data like blobs. Similarly, setting contentType to false allows the browser to determine the appropriate content type for the upload.

Custom Implementation

If you prefer to create an XHR (XMLHttpRequest) object manually, you can use the following steps:

1. Initialize a new XMLHttpRequest object:

var xhr = new XMLHttpRequest();

2. Set the method, URL, and request headers:

xhr.open('POST', '/upload.php', true);
xhr.setRequestHeader('Accept', 'application/json');

3. Create a FormData object and append the data:

var fd = new FormData();
fd.append('fname', 'test.wav');
fd.append('data', soundBlob);

4. Send the FormData as the request body:

xhr.send(fd);

5. Handle the server response in the onload event:

xhr.onload = function() {
    var data = JSON.parse(xhr.responseText);
    console.log(data);
};

By following these steps, you can efficiently upload blobs to a server using JavaScript, enabling you to process and store multimedia data effectively.

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