How to Create a Blob from a Base64 String in JavaScript?

Creating a Blob from a Base64 String in JavaScript

The Problem

You have base64-encoded binary data in a string and want to create a Blob URL containing this data and display it to the user. Specifically, the goal is to create a Blob object from the base64 string, as seen in the code snippet below:

const blob = new Blob(????, {type: contentType});
const blobUrl = URL.createObjectURL(blob);

The Solution

To decode a base64 string to a Blob object in JavaScript, follow these steps:

1. Decode the base64 data: Use the atob function to decode the base64 string into a character string:

   const byteCharacters = atob(b64Data);

2. Convert byte characters to byte values: Create an array of byte values by getting the character code point (charCode) for each character in the string:

   const byteNumbers = new Array(byteCharacters.length);
   for (let i = 0; i 

3. Create a typed byte array: Convert the byte values into a real typed byte array using the Uint8Array constructor:

   const byteArray = new Uint8Array(byteNumbers);

4. Wrap in an array and create Blob: Create a Blob object by wrapping the byte array in an array and passing it to the Blob constructor:

   const blob = new Blob([byteArray], {type: contentType});

Performance Optimization

The code above is fully functional, but performance can be improved by slicing the byte characters into smaller chunks before processing.

Full Example

Here's a full example, creating an image element from the Blob:

const b64toBlob = (b64Data, contentType='', sliceSize=512) => {
  const byteCharacters = atob(b64Data);
  const byteArrays = [];

  for (let offset = 0; offset 

The above is the detailed content of How to Create a Blob from a Base64 String in JavaScript?. For more information, please follow other related articles on the PHP Chinese website!