Isomorphic JavaScript Applications — the Future of the Web?

    Aurelio De Rosa

    One of the best known mottos around the web is Java’s Write once, run everywhere. But does this motto apply to Java only? Can we use it to describe JavaScript too? The answer is Yes.

    In this article, I’ll introduce you to the concept of isomorphic JavaScript applications, describing what they are and pointing to resources that help you develop this kind of application.

    How We Arrived Here

    Many years ago, the web was a bunch of static pages made with HTML and CSS without much interactivity. Each user action required the server to create and serve a complete page. Thanks to JavaScript, developers started to create nice effects, but it was with the advent of Ajax that a revolution started. Web developers began to write code that could communicate with the server to send and receive data without the need to reload the page.

    As the years have passed, the responsibilities of the client-side code have grown a lot, resulting in a new type of application known as the single-page application (SPA). In an SPA, all the necessary assets are retrieved with a single page load, or dynamically loaded and added to the page as necessary. Some examples of SPAs are Gmail and the StackEdit editor.

    SPAs allow for better interactivity, because almost all their operations are executed on the client, keeping communications with the server to a bare minimum. Unfortunately, they also have some major problems. Let’s discuss some of them.


    Because SPAs require more client-side code than static pages, the amount of data to download is increased. This leads to slower initial loading times, which can have drastic consequences – such as frustrated end users and loss of revenue. According to one Microsoft article

    A Bing study found that a 10ms increase in page load time costs the site $250K in revenue annually.


    Because single-page applications rely on JavaScript execution, servers don’t produce all the HTML content they used to. Therefore, web crawlers have a lot of difficulties indexing pages. These crawlers are programs that make requests to a web server and analyze the result as raw text, without interpreting and executing the content like a typical browser running JavaScript would do. Recently, Google improved its web crawler so that it can work with JavaScript-based pages, but what about Bing, Yahoo, and all the other search engines? Good indexing is crucial for any business, as it usually leads to more visits and higher revenue.

    Isomorphic JavaScript Applications

    Isomorphic JavaScript applications are applications written in JavaScript that can run both on the client and on the server. Because of this, you can write the code once and then execute it on the server to render static pages and on the client to allow for fast interactions. So, this approach takes the best of the two worlds and lets you avoid the two issues described before.

    Today there are several frameworks that assist you in developing this kind of application. One of them – possibly the most well-known – is Meteor. Meteor is an open-source JavaScript framework, written on top of Node.js, that focuses on real-time web applications. Another project I want to mention is Rendr. It’s a small library developed by Airbnb that allows you to run Backbone.js applications on both the client and the server.

    More companies are adopting Node.js for their products. Sharing code between the client and server is becoming a more common and natural choice, and in my opinion is the future of web development. This trend is enhanced by sharing templates through libraries like React.


    In this article I’ve introduced you to the concept of isomorphic JavaScript applications, a new approach to developing applications that combines the best of server-side and client-side programming. We’ve also discussed what problems this approach tries to solve, and some projects that you can employ today to embrace this philosophy.

    Had you already heard of isomorphic JavaScript applications? Have you developed one? What was your experience?