Blob objects are used to process immutable raw data in the browser and are often used for binary data operations such as files and pictures. 1. You can create downloadable files; 2. Read content through FileReader; 3. Upload files through FormData; 4. Create the object URL to display the picture directly. Each blob contains size and type attributes. The creation method is new Blob(dataArray, {type}), which can combine multiple segments of data. The ways to read or use a blob include: 1. URL.createObjectURL() generates a URL; 2. FileReader reads the content; 3. Send to the server through fetch. Blob itself has simple functions, but it has become the core tool for processing files with other APIs.

The Blob object in JavaScript is a built-in data structure that represents immutable raw data. It's often used to handle binary data such as files, images, audio, or video in the browser. You might encounter Blobs when working with file uploads, downloading content from APIs, or manipulating media.

What can you do with a Blob?

A Blob gives you a way to work with chunks of data without needing to load everything into memory at once. Here are some common uses:

• Create downloadable files on the fly
• Read and manipulate file content using FileReader
• Upload files through FormData and fetch
• Display images directly in the browser by creating an object URL

Each Blob has a .size (in bytes) and a .type (like image/png or text/plain ), which helps you understand what kind of data it contains.

How to create a Blob

Creating a Blob is straightforward. You pass it an array of data and optionally a type:

 const text = 'Hello, world!';
const blob = new blob([text], { type: 'text/plain' });

You can also combine multiple pieces of data:

 const data1 = 'Part one';
const data2 = new Uint8Array([72, 101, 108, 108, 111]); // "Hello" in ASCII
const blob = new Blob([data1, data2], { type: 'text/plain' });

If you want to see the contents of a Blob, you'll need to use a FileReader or convert it into a URL.

How to read or use a Blob

Since Blobs hold raw data, you usually need to process them before displaying or sending them somewhere. Here are a few typical approaches:

• Convert to a URL : Use URL.createObjectURL(blob) to display images or let users download files.

   const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = 'hello.txt';
  a.click();

• Read contents with FileReader : Useful for inspecting or modifying data.

   const reader = new FileReader();
  reader.onload = function(event) {
    console.log(event.target.result); // The content as a string
  };
  reader.readAsText(blob);

• Send via fetch : Append to FormData or send directly in a POST request.

   const formData = new FormData();
  formData.append('file', blob, 'filename.txt');
  
  fetch('/upload-endpoint', {
    method: 'POST',
    body: formData
  });

  These methods make Blobs flexible for both client-side processing and communication with servers.

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  Basically, the Blob object is a simple but powerful tool for handling binary data in web applications. It doesn't do much on its own, but paired with other APIs like FileReader, URL, or fetch, it becomes essential for many file-related tasks.

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