Understanding Dependencies

Modern software is built on the shoulders of giants. You’re rarely writing everything from scratch. Instead, you’re using libraries (dependencies) to do things like talk to a database, handle authentication, or format dates.

Where to Find Them

Different languages use different files to list their dependencies:

• JavaScript/TypeScript: package.json
• Python: requirements.txt or pyproject.toml
• Ruby: Gemfile
• Go: go.mod
• Rust: Cargo.toml

Step-by-Step: Reading a package.json

When you open a package.json, focus on these two sections:

1. dependencies: These are required for the app to run in production (e.g., react, express, mongoose).
2. devDependencies: These are only used during development (e.g., jest for testing, eslint for formatting).

    Project Stack
    +--------------------------------+
    | Frontend Framework: React      |  <-- In dependencies
    | UI Library: Tailwind CSS       |  <-- In dependencies
    | Data Fetching: Axios           |  <-- In dependencies
    | Testing Tool: Jest             |  <-- In devDependencies
    +--------------------------------+

Practical Strategy: The “What is this?” Google

If you see a dependency you don’t recognize:

1. Search for it on the web: “npm axios” or “python pandas.”
2. Read the first paragraph of its documentation: What problem does it solve?
3. Search for its usage in your codebase: Where is it imported? How is it being used?

Real-World Example: A Surprise Discovery

You’re looking at a bug related to dates. You check package.json and see date-fns listed. You now know to search the codebase for imports from date-fns to find where the date logic lives.

Mental Model: The Lego Box

Think of a project like a finished Lego set. The dependencies are the different types of bricks (square, thin, wheels, motors) used to build it. To understand the whole set, you need to know what the individual bricks do.

Common Mistake: “Blind Trust”

Just because a library is in the dependencies list doesn’t mean it’s being used. Sometimes projects have “ghost dependencies”—old libraries that were never removed. Always verify usage before assuming a library is active.

Next: Debugging While Reading Code