react-native-blob-util

Charlotte

3 min read

·

28-02-2025

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React Native's file handling capabilities can sometimes feel limited, especially when dealing with complex binary data like images, videos, or PDFs. This is where react-native-blob-util steps in. This powerful library provides a robust and flexible way to manage Blob objects—binary large objects—within your React Native applications. This article will explore its functionality, usage, and best practices.

Understanding Blob Objects and Their Importance

Before diving into react-native-blob-util, let's briefly understand what Blob objects are. A Blob is a raw binary data object, representing files or parts of files. They're essential for handling various file types in a browser-independent way. In React Native, dealing with blobs allows you to:

• Download and upload files: Easily manage file transfers with servers.
• Process image data: Manipulate images before uploading or displaying.
• Handle various file formats: Work with PDFs, videos, and more, beyond standard React Native limitations.
• Improve performance: Efficiently manage large files without loading them entirely into memory.

Installing react-native-blob-util

Adding react-native-blob-util to your project is straightforward. Use npm or yarn:

npm install react-native-blob-util
# or
yarn add react-native-blob-util

For iOS, you might need to add a bridging header file. Consult the library's documentation for specific instructions.

Core Functionality of react-native-blob-util

The library offers a comprehensive set of functions for Blob manipulation:

1. Creating Blobs

You can create Blobs from various sources:

• From a URL: Download a file and convert it to a Blob.

import RNFetchBlob from 'react-native-blob-util';

RNFetchBlob.config({
  fileCache: true,
  appendExt: 'jpg', 
})
  .fetch('GET', 'https://example.com/image.jpg')
  .then((res) => {
    // res.data represents the Blob
    console.log('Blob downloaded:', res.data);
  })
  .catch((err) => {
    console.error('Error downloading Blob:', err);
  });

• From a base64 string: Convert a base64 encoded string into a Blob.

const base64String = 'data:image/png;base64,...';
const blob = RNFetchBlob.base64.decode(base64String);

• From a file: Create a Blob from a file path.

const filePath = '/path/to/your/file.pdf';
RNFetchBlob.fs.readFile(filePath, 'base64')
    .then((base64Data) => {
       // Convert the base64 string to a Blob as shown above.
    })
    .catch(err => console.log(err));

2. Working with Blobs

Once you have a Blob, you can perform various operations:

• Upload Blobs: Send Blobs to a server.

RNFetchBlob.fetch('POST', 'https://example.com/upload', {
    'Content-Type': 'multipart/form-data',
}, [
    { name: 'image', filename: 'image.jpg', type: 'image/jpeg', data: blob }, // blob is your Blob object.
])
.then((res) => {
  console.log("Upload successful", res.data)
})
.catch((err) => {
  console.log("Upload failed", err)
})

• Saving Blobs: Save Blobs to the device's file system.

const filePath = RNFetchBlob.fs.dirs.DocumentDir + '/myImage.jpg';
RNFetchBlob.fs.writeFile(filePath, blob, 'base64')
    .then(() => {
        console.log('Blob saved successfully to:', filePath);
    })
    .catch((error) => {
        console.error('Error saving Blob:', error);
    });

3. File System Access

react-native-blob-util provides extensive file system access functions, allowing you to:

• Read files.
• Write files.
• Create directories.
• Delete files and directories.
• And much more.

Advanced Usage and Considerations

• Error Handling: Always include robust error handling to manage potential issues during file operations.
• Progress Monitoring: For large files, consider implementing progress monitoring to inform the user about the download or upload status.
• Permissions: Ensure you have the necessary file system permissions on both iOS and Android.
• Caching: Use the fileCache option to efficiently manage downloaded files.

Conclusion

react-native-blob-util is a vital tool for any React Native developer working with binary data. Its comprehensive API allows for easy management of Blobs, simplifying file handling tasks and enhancing the capabilities of your applications. Remember to consult the official documentation for the most up-to-date information and examples. By mastering this library, you'll significantly improve your ability to build robust and feature-rich React Native applications.