Express res.download() Method

Posted in Express Tutorial

Updated on Oct 28, 2024

By Mari Selvan

👁️ 120 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

File downloads are a common requirement in web applications, and Express.js simplifies this process with the res.download() method. This powerful feature allows you to initiate file downloads seamlessly.

In this guide, we'll explore the syntax, usage, and practical examples of the res.download() method, providing you with the tools to enhance file handling in your Express.js applications.

💡 Syntax

The syntax for the res.download() method is straightforward:

syntax.js

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res.download(path [, filename] [, options] [, callback])

path: The file path on the server.
filename (optional): The name to suggest to the user when saving the file.
options (optional): Additional options, such as headers.
callback (optional): A callback function to be executed after the file is sent.

❓ How res.download() Works

The res.download() method prompts the user to download a file from the server. It sets the appropriate headers for file download and handles any errors that may occur during the process.

example.js

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app.get('/download', (req, res) => {
  const filePath = '/path/to/your/file.txt';
  res.download(filePath, 'custom-filename.txt', (err) => {
    if (err) {
      // Handle errors, such as file not found
      res.status(404).send('File not found');
    }
  });
});

In this example, accessing the /download route triggers a file download with a custom filename.

📚 Use Cases

Secure File Downloads:

Leverage res.download() to ensure that file downloads are secure by implementing authentication and authorization checks.

example.js

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app.get('/secure-download', (req, res) => {
  const filePath = '/path/to/secure/file.pdf';

  // Perform authentication or authorization checks before allowing the download
  if (/* authentication or authorization logic */) {
    res.download(filePath, 'document.pdf');
  } else {
    res.status(401).send('Unauthorized');
  }
});

Serving Dynamic Files:

Use res.download() to serve dynamically generated content by creating a temporary file.

example.js

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app.get('/dynamic-download', (req, res) => {
  const dynamicContent = generateDynamicContent(); // Your logic to generate dynamic content

  // Create a temporary file with dynamic content
  const tempFilePath = '/path/to/temp/file.txt';
  fs.writeFileSync(tempFilePath, dynamicContent);

  // Initiate download with the temporary file
  res.download(tempFilePath, 'dynamic-file.txt', (err) => {
    // Clean up the temporary file after download
    fs.unlinkSync(tempFilePath);
    if (err) {
      res.status(500).send('Internal Server Error');
    }
  });
});

🏆 Best Practices

Error Handling:

Implement robust error handling to address scenarios like file not found or internal server errors during the download process.

example.js

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app.get('/download', (req, res) => {
  const filePath = '/path/to/your/file.txt';
  res.download(filePath, (err) => {
    if (err) {
      // Handle errors, such as file not found
      if (err.code === 'ENOENT') {
        res.status(404).send('File not found');
      } else {
        res.status(500).send('Internal Server Error');
      }
    }
  });
});

Setting Custom Headers:

Adjust headers as needed, such as controlling caching behavior or specifying content type.

example.js

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app.get('/download', (req, res) => {
  const filePath = '/path/to/your/file.txt';
  
  // Set custom headers
  const options = {
    headers: {
      'Content-Type': 'application/octet-stream',
      'Content-Disposition': 'attachment; filename="custom-filename.txt"',
    },
  };

  res.download(filePath, options, (err) => {
    if (err) {
      // Handle errors
      res.status(500).send('Internal Server Error');
    }
  });
});

🎉 Conclusion

The res.download() method in Express.js provides a streamlined way to facilitate file downloads in your web applications. Whether you're serving static files or dynamically generating content, incorporating res.download() enhances user experience and simplifies file handling.

Now, armed with knowledge about the res.download() method, go ahead and implement efficient file downloads in your Express.js projects!