Web Development

A Guide to Legacy Application Modernization with React

Published: 5th February, 2024

Tapash Kumar Mahato

Web Development Consultant at almaBetter

Revamp legacy applications with React for seamless modernization, boost performance, and stay competitive through Legacy Application Modernization expertise.

Since the modern era of business needs constant change and update, to cope with the speed and demand of business, applications need modernization.

An example of the modernization with React is Dropbox: file sharing with React.

Dropbox, a popular cloud-based file-sharing service, switched to React a couple of years ago. As of 2023, 600 million users and 1.2 billion files are uploaded daily by this platform.

The decision to switch to React was made to accommodate the massive traffic and data flow, as well as to allow for fast growth and easy scaling. With React, Dropbox can take advantage of features like code components to increase the efficiency of development, which helps the platform grow even faster.

Dropbox started in 2007 intending to design a simpler way to keep files in sync. Today, they design products that reduce busywork so that users can focus on the work that matters.

What is a Legacy Application Modernization?

It is a process where the applications built using older technologies are modified by implementing new upgrades and improving the functionality, performance, and maintainability of existing legacy applications written in different technologies.

How does an application qualify for modernization?


These are a few points -

  • Support and maintenance are limited to a certain limit.
  • Since they are based on outdated technology, hence incompatible with modern or more advanced solutions.
  • Are not available to purchase
  • Cause issues in the process of development

Why React?

React is a popular front-end JavaScript library for building user interfaces based on components. React can be used to develop single-page, mobile. It is widely used in web development to create interactive user interfaces and is known for its efficiency and performance.

Features of React are:

  • Component-based architecture: It follows a component-based architecture, where the UI is divided into reusable components that can be easily managed and maintained.

  • JSX syntax: JSX stands for JavaScript XML, It allows developers to write HTML-like code within JavaScript, making it easier to visualize and understand the structure of the UI components.

  • Modern JavaScript features: It utilizes features of modern JavaScript, such as ES6 and beyond, for many of its patterns, including features like arrow functions, destructuring, and spread operators, which make the code more concise and efficient.

  • Community-driven: This community-driven approach allows for continuous improvement, innovation, and a rich ecosystem of libraries and tools.

  • Easy to learn: It has a short learning curve compared to other frameworks, hence developers get started quickly and build projects in a relatively short time.

How to Modernize Legacy Applications, including Legacy Modernization

  1. Analyze your problems and readiness: The first step in modernizing a legacy application is to analyze problems, define goals, and prepare for the upgrade process.

  2. Systematize problems: Analyze and define the problems you want to solve. Clearly identify the main reasons for the upgrade and be fully prepared for the process.

  3. Create an action plan, risks, and budget: To upgrade the application, create a detailed plan for team members, future integrations, and risk mitigation. Set a budget for the modernization project.

Using React in Modernization

Web application development is a fast-evolving field that presents many challenges. To keep up with these changes and enhance user experience, it's important to leverage modern UI frameworks such as React; however, transitioning to these new frameworks can be daunting for many developers. Fortunately, these frameworks have become the preferred choice for many web apps, helping address challenges associated with developing web apps that are Isometric, Progressive, Universal, and Native using the same core frameworks, including legacy modernization.

For example, one application which is 15 years old, named Uyuni, and the upstream community extends from which the widely utilized SUSE Chief is determined. It is not surprising that an application that has been in use for a long time would have accumulated a vast number of outdated technologies and an extensive codebase. React is chosen by developers to modernize their UI and technology stack in Uyuni. It is easy to integrate into existing applications, with the ability to add it as many times as needed on a page. They gradually introduced independent React trees to implement new features and refactor old UI parts, showcasing the importance of legacy modernization in the ever-evolving landscape of web development.

Using React in Modernization

In the earlier days of web development, server-side rendering was the standard way to render information to the client. Developers would use Java and JSP to return initial HTML code that embedded JavaScript which is executed on the client.

However, modern web development has shifted towards client-side rendering, where a large part of the page is rendered in the browser first using JavaScript, provided the user has not blocked it. This approach relieves the server by reducing the number of requests made and ensures fast delivery of content.

Server-side rendering, on the other hand, permits designers to pre-populate a web page with custom client information specifically on the server.

This is done by writing code that executes on the server and fills up the HTML components. The HTML page then displays the information on the server, and the same code executes on the client when it needs additional information.

This approach is generally faster than making extra browser-to-server round trips, as all the requests are made within the server.

However, implementing server-side rendering can be challenging, and it requires developers to share code between the server and client to ensure that the same code executes on both.

We can have a local webpack server recompiling our JavaScript changes and hot updates. This way we can serve all the overhauled records from our neighborhood environment, but still, intermediary everything that isn’t front-end related and depends on a back-end server.

It can be a neighborhood advancement server or a further shared test server. In this way, on the off chance that you merely have to work on the front end, there's no ought to introduce the total back conclusion as some time recently, and you'll still be able to appreciate all the magnificent web pack/hot-reload highlights.


In conclusion, modernizing legacy web applications with React can be a challenging task, although providing a better user experience is essential for organizations to stay competitive. The integration of React components into legacy codebases can be achieved through custom elements, and modernization can also be accomplished one component at a time through React hooks.

Fully automated migration using refactoring technology can also be a more efficient option for legacy modernization. While there may be cost, risk, and disruption associated with modernization approaches, the benefits of a more efficient and effective system can outweigh the challenges. Ultimately, modernizing legacy web applications with React can help companies stay relevant in today's fast-paced digital landscape.

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