Understanding a codebase is a complex process that involves learning how an existing software system works without prior knowledge of its inner workings. To help you with this problem, I have created 12 step framework to tackle any codebase with few advices :

1) Set your objective:

Determine why are you going to understand the codebase. Are you looking to understand its functionality, find bugs, improve performance, or gain insights for integration with other systems? This step is very beneficial as it helps you in:

• Efficiency: Knowing what you need to understand allows you to prioritize your time and effort, making the process more efficient.
  • Focused Learning: Having a clear objective helps you concentrate on specific parts of the codebase relevant to your goals. This avoids getting overwhelmed by the entire codebase. Having a clear objective helps to focus on relevant parts of the codebase, avoiding unnecessary details that are not aligned with the goal.
  • Goal Alignment: Ensures that your understanding aligns with the specific goals of your project or task, whether it’s debugging, adding features, or refactoring.
  • Documentation Navigation: Guides you in navigating through the documentation and other resources more effectively, focusing on the sections that matter most to your objective.
  • Better Questions: With a clear objective, you can ask more targeted and relevant questions when seeking help online or with others.
  • Progress Tracking: Setting an objective allows you to measure your progress and determine whether you are on the right track towards understanding and achieving your goal.

2) State the purpose of project (that codebase represents):

State clearly and in-details, what that codebase is for, how it is being used, what it is serving. By doing so, this will help you in:

• Efficient Use of Time: Knowing the purpose helps prioritize which sections of the code are most critical to review and understand, leading to a more efficient use of time.

  • Improved Contextual Understanding: It provides the necessary context to understand why certain decisions were made, such as design patterns, architecture choices, and specific implementations.
  • Focused Analysis: Understanding the purpose provides a clear direction, helping to focus on relevant parts of the codebase rather than getting lost in unnecessary details.

  But, what to do when objective of codebase is not self-evidence or clear. To solve this problem; Gather any available documentation or resource, such as user manuals, design documents, API documentation, and comments within the code. These resources can provide valuable context and save time. Analyze code comments ; Pay close attention to comments within the code itself, as they often contain insights into the code's purpose and functionality. But even if codebase objective is clear you should gather information resources.

After completing these two steps, its time to get big picture overview of the codebase as it will help us to grasp the overall structure, design patterns, and key components.

3) Explore project structure:

• Understand the Directory Hierarchy: Begin by examining the project's folder structure to get an overview of how the codebase is organized. Key directories to look for include are:

  • src (Source): Contains the main application code, including modules, classes, and functions.
  • public: Holds public assets like HTML files, images, and other resources accessible directly via the web server.
  • components: Typically used in front-end projects to house reusable UI components.
  • tests or specs: Contains unit tests, integration tests, and other testing-related code.
  • build or dist: Holds the compiled or bundled output of the project, ready for deployment.
  • docs: Includes documentation related to the project, such as README files, API docs, and design documents.

• Configuration files provide critical information about how the project is set up, built and run. Key configuration files to examine include package.json, webpack.config.js and .env :
  
  - package.json: Found in Node.js projects, it lists project dependencies, scripts for common tasks (e.g., start, build, test), and metadata about the project.
  
  - webpack.config.js or rollup.config.js: Configuration for module bundlers, detailing how the project's files are compiled and packaged.
  
  - .env or .env.local: Environment variable configurations that store sensitive information and environment-specific settings.

4) Identify the Entry Point:

• Locate the Main Entry Point: Find the primary starting point of the application where execution begins. This could be a main() function in languages like C/C++, an App.java file in Java, or an index.js file in a Node.js project. Identifying the entry point provides a foundational understanding of how the application initializes and starts its operations.

  • Understand Initialization Logic: The entry point often contains critical initialization logic, such as setting up configurations, initializing dependencies, and starting services. By examining this code, you can gain insight into the application's initial setup and how different components are wired together.
  • Follow Execution Flow: From the entry point, trace the flow of execution to understand how the program proceeds. Identify the key functions or methods that are called next, and follow the sequence of operations to get a sense of the application's structure and logic.

5) Evaluate the Architecture:

• Examine the Overall Architecture: Understand the architectural style employed by the project, such as monolithic, microservices, layered, or event-driven. Determine how the application is organized into various modules, services, or layers and how these components interact.

• Identify Architectural Patterns: Look for common architectural patterns (e.g., MVC, MVVM, Singleton, Factory) and design principles used throughout the codebase. This can provide insights into the intended design and interactions within the codebase.

This holistic view will help you prioritize your efforts.

6) Analyze dependencies:

• Check Package Managers: If the project uses package managers (like npm for Node.js or Composer for PHP), review the dependency files to understand the libraries and frameworks used.
  • Explore Third-Party Libraries: Familiarize yourself with any third-party libraries included in the project. Check their documentation to understand how they are integrated.
  • APIs and Services: Identify any third-party APIs or services the website integrates with and understand how they are used.
  • Libraries and Frameworks: Look at external libraries and frameworks and their roles in the project.

7) Establish a hierarchy by Identify Critical (key) Components :

• Core Functionality: Pinpoint the core components that provide essential functionality for the application. These might include key modules, services, controllers, or classes that are central to the application's operation.
  • Infrastructure Components: Identify components responsible for infrastructure-related tasks such as database access, authentication, logging, and error handling.

Once you get the big picture of the codebase and have information about codebase’s structure, components’ hierarchy and codebase’s purpose, its time to utilize these knowledge to:

8) Create user and programmer stories according to codebase:

If it is a codebase of a software or app that which users can interact with, then create user stories.

• Create User Stories: take the time to document user stories that detail how users interact with the software. These stories should capture specific user actions, goals, and the pathways they follow within the application. By doing so, you not only clarify the purpose of various components but also illuminate their intended functionality within the broader user experience. This process helps you see the software from the user’s perspective, making it easier to understand the overall design and flow of the application. Furthermore, user stories can reveal the rationale behind certain design choices, aiding in the identification of key features and their interdependencies, ultimately making the codebase more approachable and navigable.

If that’s not the case and it is some Legacy Codebases then, create programmer stories

• Create Programmer Stories: document programmer stories that describe how the original developers constructed and organized the application. This involves understanding their thought processes, rationale behind architectural decisions, coding patterns, design choices they made and the evolution of the code over time. By tracing the thought process behind the code, you can gain insight into the developer's mindset and the challenges they faced, why certain approaches were taken, what challenges were addressed, which will help you comprehend the structure, purpose, and functionality of the code more effectively and how they fit into the broader architecture. This practice is invaluable for unraveling complex codebases and preserving the context behind key implementation choices.

  Both can be done in appropriate situation.

Now that you are done with this step, its to delve into details. Read the code thoroughly: Begin by examining the code line by line. Take detailed notes to build a mental model of its functionality and flow. Understanding the logic behind the code is essential for any modifications or enhancements you plan to make. Keep detailed notes of your observations, including the purpose of key functions, data structures, and algorithms. Diagrams can help visualize complex interactions.

9. Map the Application Flow:

• Trace the Data Flow:
  • Follow the Data Path: Examine the journey of data through the application from input to output. Identify key stages where data is received, processed, transformed, and eventually stored or presented.
  • Locate Data Processing Points: Locate and understand critical points where data is manipulated, such as in functions, methods, or services that handle core logic and transformations.
  • Track Variable Assignments and Function Calls: Track how data is passed through different parts of the application by following variable assignments and function calls. This helps in understanding how data is manipulated and transferred across various components.
  • Pay Attention To Database Interactions: Pay close attention to how the application interacts with databases. Understand how data is queried, inserted, updated, and deleted, and identify the key database operations and their role in the data flow.
• Understand Control and Logic Flow:
  • Do Control Flow Analysis: Analyze the flow of control through the application, focusing on major workflows and processes. Determine how different components and modules interact and the sequence of operations.
  • Map out User Interactions: Map out how user actions and events are handled. Understand the flow from user input (e.g., button clicks, form submissions) to the corresponding application responses and updates.
  • Nail down Business Logic: Trace the core business logic that drives the application's functionality. Identify key functions and methods that encapsulate this logic, and understand how they interact with other parts of the system.
  • Examine Component Communication: Examine how different components communicate with each other, including inter-process communication, API calls, and messaging between services. This helps in understanding the overall architecture and integration points.
• Visualize the Flow:
  • Make Flow Diagrams: Create visual representations such as flowcharts, sequence diagrams, or data flow diagrams to illustrate the flow of data and control within the application. These visual aids can help in quickly grasping complex flows and identifying potential bottlenecks or inefficiencies.
  • Do Event Tracing: Map out event flows to understand how events are propagated and handled throughout the system. This includes user events, system events, and asynchronous operations.

At this point, you will have solid understanding of the codebase. Now, its time to test what you have learned. To do that:

10) Set Up the Environment:
- Ensure you have the necessary development environment to compile and run the code. This may involve setting up specific versions of programming languages, libraries, and tools.

11) Test hypotheses, modify and experiment:
- Experiment with Small Changes:
- Validate Your Understanding: Make minor modifications to the codebase to test your understanding of its behavior. For instance, change a variable value, adjust a condition in an if-statement, or modify a function's implementation. Observe how these changes impact the overall application to confirm or refine your comprehension.
- Analyze Effects: Carefully analyze the effects of your changes on the application's functionality. Pay attention to both expected and unexpected outcomes, as they can provide valuable insights into how different parts of the codebase are interconnected.
- Hands-on Enhancement and Fixes:
- Implement Small Enhancements: If your objective is to improve the code, start with small, incremental changes. This could involve optimizing a function, refactoring a piece of code, or enhancing a feature. Gradually build on these changes as you gain confidence in your understanding.
- Utilize Version Control:
- Track Changes with Git: Use Git or another version control system to track your modifications. Commit your changes frequently with descriptive messages, detailing what was changed and why. This practice helps in maintaining a clear history of your work.
- Create Branches for experiment: Work on separate branches for different experiments or enhancements. This allows you to isolate your changes and test them independently without affecting the main codebase.
- Revert Changes When Necessary: If a change leads to unintended consequences or breaks the application, use Git to revert to a previous stable state. This safety net encourages experimentation without the fear of causing irreversible damage.

12) Review similar codebases:

• Study Open-Source Projects:
  • Identify Relevant Projects: Search for open-source projects that are similar in scope, technology stack, or functionality to the codebase you are working on. Platforms like GitHub, GitLab, and Bitbucket are excellent resources for finding such projects.
  • Analyze Common Patterns: Examine these projects to identify common architectural patterns, coding conventions, and best practices. Look for how these projects structure their code, manage dependencies, handle data flow, and implement core functionalities.
• Understand Problem-Solving Approaches: (not)
  • Solution Strategies: Observe how similar problems are addressed in other projects. Compare different approaches to solving the same problem to understand the trade-offs and benefits of each method.
  • Optimization Techniques: Pay attention to optimization techniques used in other codebases, such as performance improvements, resource management, and scalability enhancements.

Aside from these steps, it is also important to:

Seek Help and Resources

If you encounter challenges, consider reaching out to online forums or communities (like Stack Overflow) and LLMs for assistance. Utilize official documentation for any frameworks or libraries used in the project to clarify functionality and best practices.

Last advice:

But even if you follow all these step, there is high chance that your retention of all these information will be low. And how we even properly synthesis and organize all of this information without getting overwhelmed. To do that I recommend to make mind-map.

Group all the modules, components, or code blocks based on their functionality, behavior, and implementation. Consider how all these groups relate to each other, such as through cause-and-effect relationships, chronological sequences or conceptual links. Express these relationships clearly in your mind map.

Use symbols instead of words to represent different elements and ensure the mind map has a clear direction or flow. Utilize arrows to demonstrate how the ideas in your mind map interact with each other. Emphasize the most important parts of the mind map by indicating clear and deliberate judgments about their significance. This will help in visually distinguishing the priority and relevance of various components within the codebase.

Happy coding!