A Quick Intro to Dependency Injection: What It Is, and When to Use It

Dependency injection (DI) is an ever-growing trend in custom software development nowadays. It is gaining widespread popularity due to its ability to reduce boilerplate code, thus, making the development and testing process more efficient and hassle-free.

Although this programming technique may seem too complicated to understand initially, it’s a fundamentally simple pattern. In this article, we will provide you with an insight into what dependency injection is, its core characteristics, and the peculiarities of dependency injection for Vue.js.

What Is Dependency Injection?

Before getting into dependency injection (DI), it’s necessary to understand what dependency itself is. Dependency is a term in programming used to describe a situation when one piece of software relies on another one, thus, can’t run without it. In other words, if one class uses some functionality of another one, it means that it has a dependency on that class. Therefore, dependency injection is a design pattern where an object supplies dependencies for another object.

This design technique includes three types of classes: client class or dependent class, service class or dependency class, and injector class that inserts service class object into the client class. The injection class can inject dependencies into a client class in three ways:

1. Through a constructor when a dependency is injected through a dependent class constructor.
2. Through a property when a dependency is supplied through a public property of a dependent class.
3. Through a method when a dependent class uses an interface that declares the method to supply dependency, and the injector implements this interface to supply the dependency to a dependent class.

DI stands behind the Dependency Inversion (DIP) principle which states that the class’s main task is not to create necessary objects to perform its functions but to fulfill its core responsibilities. There comes DI, providing the class with the required objects.

Why Should You Use Dependency Injection?

Here are some of the DI key benefits, helping developers build more robust, scalable, and efficient applications that will be easier to test and maintain in the future.

• Loose coupling. DI enables loose coupling which reduces the risks that alterations in some elements will cause unpredicted changes in other parts of the program. It is an effective solution to make the code more maintainable, thus, simplify testing and troubleshooting procedures.
• Code simplification. Dependency injection helps to reduce boilerplate code since dependencies are initialized by the injector.
• Exception management. DI allows developers to inject exception management logic, which means that they don’t have to write similar logic for each development phase.
• Improved scalability of the apps. DI makes it easier to extend apps since it allows adding new functionalities to dependencies separately.
• Unit testing. This design pattern facilitates unit testing due to increased class independence and simplified mocking.
• Independent development. Dependency injection lets two or more developers build classes simultaneously or independently from each other, knowing only the interface the classes will use.

Although DI’s advantages outweigh its disadvantages, to implement this pattern effectively it’s crucial to be aware of its drawbacks.

• Steep learning curve. This technique is often considered to be quite complicated. Moreover, once overused it may cause some management issues.
• Challenging troubleshooting. The dynamic programming approach used by most of the DI frameworks makes the troubleshooting process more complicated.
• Configuration data. DI clients are dependent on configuration data which creates extra tasks for developers if there is no need for so many custom configuration values.
• Code tracing. DI makes it more challenging to trace the code, especially for newbies.

Libraries and Frameworks

It’s possible to implement dependency injection on your own. However, it can be tiresome, monotonous, and not effective for large-scale projects. Third-party libraries and frameworks relieve developers from the tedious creation of boilerplate code, helping them concentrate on more important functionalities. Moreover, they improve app flexibility and make it easier for developers to define how the program will operate. Some popular frameworks and libraries, supporting DI include but are not limited to:

• Spring is one of the most popular frameworks for the Java platform that offers a vast variety of features including DI.
• Unity (or Unity Container) is a lightweight, general-purpose DI container for any type of .NET apps.
• Google Guice is a Java-based DI open-source framework.
• Dagger is a compile-time DI framework for Java, Android, and Kotlin.
• Butterknife is a lightweight dependency injection library used for Android apps.

Dependency Injection in Vue.js Applications

Dependency Injection is not included in Vue.js functionalities by default. Thus, it’s not a popular technique for apps created in this JavaScript framework. However, it can be implemented in other ways to improve Vue.js app efficiency and robustness, for example, using third-party tools such as Vue Injector.

Vue Injector is an open-source library used to implement DI design patterns for Vue.js components. Apart from instances supporting dependency injection, this library includes DI for components, construction of injected components, accessibility of apps from service, and many other features. Vue Injector provides developers with the ability to use an event bus, create a service and a service factory, implement efficient solutions to transfer data, etc.

Vue Injector and other third-party tools for DI significantly facilitate the development process and allow software engineers to create easy testable and highly scalable applications in Vue.js.

Final Thoughts

Dependency injection is an efficient pattern used by many software engineers worldwide. Its overall popularity is mostly attributed to its ability to facilitate unit testing, simplify code, and make the development process more time-efficient and productive.

You can implement DI in your app manually, yet, keeping in mind that it requires some initial learning, or opt for third-party frameworks and tools that will help you take advantage of this programming design pattern with the least effort.