Isomorphic JavaScript Applications

Isomorphic JavaScript applications share JavaScript code between client and server. A perk of this is a codebase with an equal form regardless of environment, which leads to easier maintainability.

Below are key points from Building Isomorphic JavaScript Apps by Jason Strimpel. Strimpel uses an eCommerce site as a barometer for three qualities a modern web application should fulfill: 1) Should be indexable by search engines to improve SEO 2) Initial load should be fast 3) Future page should be fast

Specifically, the eCommerce page must appear in web searches to attract customers, and also load fast to keep these users on the site. Modern applications should have SEO support, distributed rendering, a single code base, an optimized page load, and a single stack.

Web Application History

A classic webpage uses HTML, Uniform Resource Identifier (URI) that shows the name of the server that will respond, and the Hypertext Transfer Protocol (HTTP) that connects everything. Everything renders on the server, then JavaScript renders this content to the browser. Of our three criteria, this fulfills the first two (indexable and fast initial load) but this method still needs to reload the entire page when routing.

An advancement came with AJAX, which focuses on fetching relevant information in the view layer. But this led to duplication and bugs via the two UI code bases.

Next up was Single Page Applications (SPA) which are entirely rendered on the client. This separates logic from data retrieval, consolidates UI to a single language, and has a low impact on servers. SPA’s are good and bad. They are good for future page loads (point three) but the initial load is sluggish because of a large-sized JavaScript file sent to the client. Furthermore, there is no SEO because SPAs use hash fragments for routing (e.g. #about). Because there is no network request, there is no SEO and search pages can’t crawl the site. The solution is to use a headless browser in PhantomJS.

The next advancement comes with Isomorphic apps. These are a union between classic and SPA. They are good for SEO with History API, distribute rendering with a low server load, have a single code base to reduce the UI cost and bug count, optimize the initial page load, and feature a single JS stack. The author warns the reader that isomorphism is not necessary if an application doesn’t need SEO, i.e. if the site is behind a login screen or internal.

Types of Isomorphic Applications

There are two kinds of Isomorphic Applications–environment agnostic and shimmed.

  • Environment agnostic is used with Node or a bundler and can run in any environment
  • Shimmed is an abstracted or filled in mapping for every environment. In this case, necessary abstractions include if-then and var.

Real Time Applications

Real time applications such as Uber or Slack push data from the server to the client while updating every client device with new data. These applications need a way to watch the database, a push tech such as Websockets or long polling emulation, and a cache to avoid repeat trips. Isomorphic API’s differ from real time with bidirectional data sync, and client simulation on the server. This is different from running SPA on the server.

  • There are the same API commands for the client and server, leading to a dry codebase with the same tests and same updates
  • Isomporphism, for example the Meteor framework, keeps the server, database, and client cache in sync
  • The server proactively sends data to the client. The server effectively simulates the client, updates the server, then sends these changes to the client


The book also discusses leaky abstractions. Generally, abstractions should not solve nonexistent problems, such as creating an API wrapper around a library in case they swap later. This may never happen! Abstractions should have an immediate value. Think longevity rather than premature decisions. Common abstractions include getting and setting cookies or redirecting requests. These encapsulate environmental specific details.

Modern Application Functionality

There is also a list of important functionalities or steps for modern web applications:

  • Routing- routers should map the URL to a function
  • Execution- should be asynchronous
  • Response/Render- should be async after execution
  • Serializing- any data retrieved in the previous steps should be part of the response
  • Deserializing- the client recreates objects and data
  • Attaching- interactive applications bind event handlers

Closing Thoughts

The book did a good job of introducing Isomorphic applications to the reader, and how they common web development problems. The author is clear in his arguments and keeps returning to them after looking at possible solutions. The last part of the book also has case studies of larger organizations using Isomorphism on their projects, including Node/React and Angular 1/Angular 2. While the high level explanation is great, more code examples are always welcome.