What is dependency?

A dependency is something that a piece of software needs in order to work correctly. It can be a library, a framework, a tool, or even another piece of code that provides functionality the main program relies on.

Let's break it down

  • Main program: The code you write or the app you run.
  • Dependency: The extra code or tool that the main program calls upon.
  • Version: Each dependency can have different releases; the program may need a specific version to avoid conflicts.
  • Package manager: A tool (like npm, pip, Maven) that helps you find, install, and manage these dependencies automatically.

Why does it matter?

Dependencies let developers reuse existing, tested code instead of reinventing the wheel, which speeds up development and reduces bugs. However, if a dependency is missing, outdated, or incompatible, the whole application can break or behave unexpectedly.

Where is it used?

  • Web development (e.g., React, jQuery)
  • Mobile apps (e.g., Android libraries, iOS CocoaPods)
  • Backend services (e.g., Express, Django)
  • Desktop software (e.g., Qt, .NET libraries)
  • Data science (e.g., NumPy, pandas)

Good things about it

  • Saves time: Leverage pre‑built functionality.
  • Improves quality: Well‑maintained libraries are often more reliable than custom code.
  • Encourages collaboration: Communities share and improve open‑source dependencies.
  • Easier updates: Updating a dependency can bring security patches and new features with minimal effort.

Not-so-good things

  • Version conflicts: Different parts of a project may require incompatible versions of the same dependency.
  • Security risks: Vulnerabilities in a dependency can affect your whole app.
  • Bloat: Unused or unnecessary dependencies increase the size of the final product.
  • Reliance on external maintainers: If a library is abandoned, you may need to find a replacement or maintain it yourself.