Refactoring Legacy Code: Steps and Best Practices

5 min readFeb 16, 2022


Legacy Code Refactoring

As your company or product grows, chances are your code has passed through several developers, and the code base is no longer neatly structured but continually patched. Having a software application that freezes, crashes, and behaves abnormally is a company’s worst nightmare.

Apart from staining your brand’s reputation, this can limit your company’s ability to scale. A decade-old generic software with crufty legacy code messes with the functionality of your software application, creating technical debt and stunting your company’s growth or worse, normal functionality.

So, what do you do when you find yourself with a clunky, outdated, and messy code, which is harder to reuse and test?

There are two options, you can either rewrite the entire code or refactor it. On one hand, rewriting is quite easy for the developers but comes at a hefty price. And on the other, you can save costs through refactoring the code, which is significantly cheaper but very difficult. The good news is that it’s possible to fix it without the need to disrupt the entire company’s internal and external processes. In this short and to-the-point article, we are going to walk you through the process of legacy code refactoring, revealing the common pitfalls and how you can dodge them.

So, What is Refactoring Legacy Code?

Refactoring legacy code is the process of improving the structure of an old or unfamiliar code without changing its functionality. The idea is to clean up lines of complex codes so you can understand or work with them better. This may include reducing redundancies or errors to make the code readable and manageable.

While refactoring a legacy code may sound similar to rewriting it, they differ.

In a code rewrite, developers would remove nearly everything to create a new code and implement new functionality from scratch. Refactoring is less extreme. Think of it like editing your old high school paper. When you review it, chances are you may find wordy sentences or repetitions that serve little use to the essay. When you improve these words without altering the meaning, that’s refactoring for programmers.

Legacy code refactoring scheme

Legacy code refactoring works on the basic principle of cleaning up the code base to improve its performance, making it readable and easy to maintain.

There are various benefits to careful refactoring legacy code. For starters:

  • It makes code easy to understand: Refactoring code involves restructuring code in such a way that a new developer can work on it with minimal difficulties. When it’s understandable, identifying and fixing bugs becomes effortless.
  • It enhances maintainability: Organized code is easy to maintain and improve. It also makes updating the code pretty much straightforward.
  • It improves an application’s performance: With less complex codes, a software application functions faster.
  • It is cost-effective: In the long run, simplified and restructured code will be efficient. It also minimizes the risk of bugs, which is time and cost-saving.

It provides technical support: Technical support allows you to use third-party APIs that improve the functionality of your enterprise application. You will also receive updates that fix bugs and repair existing security holes.

Legacy Code Refactoring vs. Code Rewriting: What to Choose

Rewriting is another solution to dealing with unmanageable codes. As opposed to testing and refactoring legacy code where a developer makes micro changes to an application, code rewriting (as the name suggests) is scraping away the code and building it again from the ground up.

So, when can you rewrite the code?

Rewriting is a viable option if you want to switch the application’s architecture dramatically. It is also the case when the application’s tech is turning obsolete, only supports previous versions of the system, and cannot integrate with advanced applications.

Take the example of AngularJS.

It was not long ago when Google discontinued support for AngularJS. As a result, companies that use the programming language for their web applications will no longer receive updates and cannot leverage third-party APIs. In this case, considering migrating AngularJS to Angular is a necessary step.

Legacy code refactoring alone won’t work here. You do need to makeover the entire application and rewrite codes afresh due to differences in frameworks.

On the other hand, who should refactor legacy code?

If the application is an integral part of business processes and stopping it will cause too much downtime, refactoring it is an excellent idea. This also applies if the primary app developers are available and can work on the software.

Pros and cons of code rewriting

Rewriting code allows you to change code, improving it however you deem fit. It also does away with legacy code that can make system integrations near impossible.

Even so, rewriting is time-consuming. Developers need to take time to understand the application, identify the must-have functionalities, and devise ways to incorporate them into the new code. Additionally, the risk of developing new bugs and defects is high.

Pros and cons of code refactoring

One of the major advantages of refactoring in a legacy code is that it can be done to any software architecture. It also improves the quality of code without unnecessary downtime, and developers can choose to isolate a specific codebase and work on it independently, which significantly minimizes development costs.

However, since refactoring does not tamper with the functionality of the application, you cannot add new features. It also requires robust skillsets to simplify the code, as the process is often complex.

When should you refactor or rewrite legacy code?

All in all, before you decide on whether to rewrite the code from scratch or refactor it, you need to scrutinize each option, choosing the most valuable strategy in terms of complexity, cost-effectiveness, and time used in the development process.

Read the full article on ModLogix.

Originally published at on February 16, 2022.




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