Blob對(duì)像用於處理瀏覽器中的不可變?cè)紨?shù)據(jù)，常用於文件、圖片等二進(jìn)制數(shù)據(jù)操作。 1. 可創(chuàng)建可下載文件；2. 通過FileReader讀取內(nèi)容；3. 通過FormData上傳文件；4. 創(chuàng)建對(duì)象URL直接顯示圖片。每個(gè)Blob包含大小和類型屬性。創(chuàng)建方法為new Blob(dataArray, {type})，可結(jié)合多段數(shù)據(jù)。讀取或使用Blob的方式包括：1. URL.createObjectURL()生成URL；2. FileReader讀取內(nèi)容；3. 通過fetch發(fā)送至服務(wù)器。 Blob本身功能簡(jiǎn)單，但配合其他API成為處理文件的核心工具。

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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