A JavaScript Blob is an in-memory object for temporarily holding binary or text data and forms the basis of the File API

 A JavaScript Blob is an in-memory object for temporarily holding binary or text data and forms the basis of the File API. You can create one from strings or ArrayBuffers and specify a MIME type in the second argument. URL.createObjectURL turns a Blob into a temporary URL, enabling image display or file downloads. With FileReader you can read the Blob as a Data URL or plain text.

In the sample, pressing a button generates a text Blob containing “Hello, Blob World!”, programmatically clicks an anchor to save it as sample.txt, then frees memory with URL.revokeObjectURL. The blob.slice method lets you extract portions, and generated URLs should always be revoked when no longer needed. Blobs work seamlessly with fetch, Service Workers, webcam recording, streaming compressed files, and more. The example runs in any modern browser with no external libraries, making it an ideal learning reference.