The Power of Dependency Injection in JavaScript

How to write cleaner, more testable code

Photo by Joshua Woroniecki on Unsplash

Dependency injection is a technique that allows you to remove hard-coded dependencies between software components. Instead of components referring directly to each other, you give components the dependencies they need through constructors or setters, making it easier to swap out dependencies without changing the components themselves.

This article will explain the benefits of using dependency injection in JavaScript, and provide examples of how to implement it in your code.

Why Use Dependency Injection?

Dependency injection leads to code that is:

• More reusable — Components depend on abstractions rather than concrete implementations. This means you can reuse them in more contexts.
• Easier to test — You can swap real dependencies with mock versions when testing.
• More maintainable — Updating a dependency only happens in one place, the component providing dependencies, avoiding cascading changes.

Constructor Injection

The simplest way to inject dependencies is through a component’s constructor:

class UserController {…