29 Apr 2019

HTTP/2 Push and HTTP Preload – 2 Techniques to Speed Up Your Page Load Speed

HTTP/2 Push and HTTP Preload are two techniques that can significantly enhance the speed and performance of your web application. Page load speed is a vital factor affecting many aspects that determine the success of modern websites. From search engine ranking to factors that enhance the site visitor experience, optimizing your site so that it loads rapidly and efficiently is crucial in today’s digitally-driven online world.

Developers and web service operators have introduced various technologies through the years that have dramatically reduced web page load speeds. From protocol enhancements to the performance improvements offered by Content Delivery Networks (CDNs), site operators have a wide variety of options at their disposal to enhance the performance of their web applications. HTTP/2 Push and HTTP Preload are two mechanisms that can significantly improve page load speeds, but what is the difference between the two and what are their advantages and disadvantages?

What is HTTP/2 Push?

HTTP/2 Push is a mechanism that allows web developers to define which assets should be loaded with the HTML document when a user’s browser requests it from the web server. This approach differs from the traditional HTTP standard where the HTML file is loaded first. Once the client interrogates the HTML document, it then requests any additional web assets such as images, stylesheets, and JavaScript files from the web server. Leveraging HTTP/2 Push, web developers can increase the efficiency of the process by sending all the relevant assets with the HTML document when the user’s browser visits the relevant web page. It optimizes the web asset delivery process as the developer can predefine and send the appropriate content with the HTML document. This process is far more efficient as it preempts the client requesting each asset individually after the initial HTML document has loaded.

What is HTTP Preload?

HTTP Preload is similar to HTTP/2 Push in that developers can proactively send web assets to their clients without the user’s browser requesting each asset after it has loaded the HTML file. However, it differs from HTTP/2 Push in that the HTML file is loaded in the traditional manner. The developer can then order the user’s browser to request high-priority assets first ensuring a consistent and enhanced user experience for the site visitor. For example, Cascading Style Sheets (CSS) and javascript files determine the look and feel of most modern websites. If these web assets are loaded late during the web page delivery process, the user’s experience is diminished. They see the raw HTML and images without the relevant styling and animation that CSS and JavaScript offer. HTTP Preload prevents these types of issues as it ensures high-priority assets are delivered first guaranteeing a consistent and engaging user experience.

HTTP/2 Push and HTTP Preload – What is the difference?

Although HTTP/2 Push and HTTP Preload both give web developers control over the web assets that get loaded with each HTML GET request, there are a few differences between these page loading mechanisms. The first difference between the two techniques is the syntax used to execute the relevant function. You can leverage preload functionality to push HTTP content, but this feature is only available if your web server or CDN is configured to support it. You can also specify preloading without HTTP/2 Push functionality by adding a ‘nopush’ variable to the HTML link tag.

Another difference between HTTP/2 Push and HTTP Preload is that with the former you can send every web asset as soon as the client requests the page. With HTTP Preload, the HTML document needs to render before initiating the preload functionality. However, preloading gives you the freedom to request web assets from third-party services. Unfortunately, this functionality is not possible with HTTP/2 Push as it only supports assets hosted on the same server and domain. Another difference between the two mechanisms is browser support. HTTP Preloading is not fully supported on all modern browsers whereas HTTP/2 Push being a part of the HTTP/2 protocol enjoys more extensive support. Finally, HTTP Preloading gives you more control of the order in which web assets are loaded. With HTTP/2 Push, the server and client control the sequence based on various factors at the time the request is made.

Leveraging HTTP/2 Push and HTTP Preload

Although both HTTP/2 Push and HTTP Preload both improve page load speeds by optimizing the delivery of web assets, there are certain circumstances where one mechanism offers a better approach than the other. Determining which of the two to use should be based on the high-priority assets that resolve to create the user experience you need for your site visitors.

HTTP/2 Push gives you the option to separate your CSS and JavaScript files from your HTML document. Instead of declaring these web assets inline, you can deliver them simultaneously to the visitor’s client instead of having them load in the traditional sequential manner. HTTP/2 Push also allows you to leverage your web server’s think time. As a browser customarily needs to wait for the HTML file to generate before it can request the assets associated with it, you can leverage this service delay to deliver the CSS and JavaScript files that complete the user experience.

HTTP Preloading should be leveraged for high-priority assets needed to ensure the best possible experience for the site visitor. It is particularly useful for more substantial web pages where you can specify preloading conditions for high-priority items such as stylesheets, images that display above the fold, and other design elements such as fonts. As preloading gives you the freedom to load these assets from third-party domains where the request time could impact the user experience, leveraging this feature can significantly enhance the overall impression your page makes on your site visitors.

Improving the User Experience with HTTP/2 Push and HTTP Preload

In today’s fast-paced, digitally-driven online economy, speed is of the essence. Users often abandon sites and pages that load slowly before the content, and your message can be delivered. It is therefore essential that you prioritize and optimize your website for speed and performance. Leveraging technologies such as a CDN and taking advantage of functionality such as HTTP/2 Push and HTTP Preload can significantly enhance your page speeds and ultimately deliver a superior user experience.