Express req.fresh Property

Posted in Express Tutorial

Updated on Feb 18, 2024

By Mari Selvan

👁️ 22 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

Conditional GET requests play a crucial role in optimizing web performance by reducing unnecessary data transfer. In Express.js, the req.fresh property is a handy tool for handling conditional requests and efficiently managing the delivery of content.

In this guide, we'll explore the syntax, usage, and practical examples of req.fresh.

💡 Syntax

The req.fresh property is a Boolean value that indicates whether the requested resource is considered fresh.

syntax.js

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if (req.fresh) {
  // Resource is fresh; send 304 Not Modified
  res.status(304).end();
} else {
  // Resource is not fresh; proceed with sending the updated content
  res.send('Updated content');
}

❓ How req.fresh Works

When a client sends a conditional GET request with the If-None-Match and If-Modified-Since headers, Express.js compares these headers with the resource's current ETag and last-modified timestamp. The req.fresh property is then set to true if the resource is considered fresh and hasn't been modified since the client's last request.

example.js

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app.get('/content', (req, res) => {
  // Check if the resource is fresh
  if (req.fresh) {
    // Resource is fresh; send 304 Not Modified
    res.status(304).end();
  } else {
    // Resource is not fresh; proceed with sending the updated content
    res.send('Updated content');
  }
});

In this example, the route handler uses req.fresh to determine whether the content should be sent or if a 304 Not Modified status should be returned.

📚 Use Cases

Efficient Resource Delivery:

Use req.fresh to efficiently deliver resources like images by avoiding unnecessary data transfer when the client already has the latest version.

efficient-resource-delivery.js

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app.get('/images/:id', (req, res) => {
  const imageId = req.params.id;
  // Check if the image is fresh before sending
  if (req.fresh) {
    res.status(304).end();
  } else {
    // Logic to fetch and send the image
    const image = fetchImageById(imageId);
    res.send(image);
  }
});

Conditional Content Updates:

Leverage req.fresh to conditionally update content only when the client requests the latest version, reducing server load and bandwidth usage.

conditional-content-updates.js

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app.get('/news', (req, res) => {
  // Check if the news content is fresh
  if (req.fresh) {
    res.status(304).end();
  } else {
    // Logic to fetch and send the latest news
    const latestNews = fetchLatestNews();
    res.send(latestNews);
  }
});

🏆 Best Practices

Set ETag and Last-Modified Headers:

Ensure your routes set appropriate ETag and Last-Modified headers for the resources. Express.js will use these headers to compare with the client's request during conditional GET.
etag.js
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```
app.get('/content', (req, res) => {
  const content = fetchContent();
  res.set('ETag', generateETag(content));
  res.set('Last-Modified', generateLastModified(content));
  res.send(content);
});
```

Combine with Caching Strategies:

Integrate req.fresh with caching strategies like client-side caching to further optimize resource delivery.

caching-strategies.js

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app.get('/styles.css', (req, res) => {
  // Check freshness and respond accordingly
  if (req.fresh) {
    res.status(304).end();
  } else {
    // Logic to fetch and send the CSS file
    const cssContent = fetchCssFile();
    res.send(cssContent);
  }
});

🎉 Conclusion

The req.fresh property in Express.js offers an efficient way to handle conditional GET requests, optimizing the delivery of resources and minimizing unnecessary data transfer. By understanding its usage and integrating it with proper headers and caching strategies, you can enhance the performance of your Express.js applications.

Now, armed with knowledge about req.fresh, go ahead and implement smart and efficient conditional GET handling in your Express.js projects!