Dependency Injection is a software design pattern which deals with how components get hold of their dependencies. In node.js, it is very common to use this pattern to manage dependencies.
The intent behind dependency injection is to achieve separation of concerns of construction and use of objects. This can increase readability and code reusability, as well as simplifying testing processes.
When we start a new Node.js project, we generally begin with a `require` at the top of our file to load dependencies. Essentially, we are making our application dependent on an outside module.
Using dependency injection, we can ‘inject’ these modules wherever necessary in our project, which is useful when our software’s components are interchangeable, as we can simply replace or mock a dependency for different environments or testing.
For example, an application may use a customer database interface that is to be injected. In production it connects to a real database while in testing it connects to a mock one.
One way to achieve Dependency Injection in Node.js is to use specialized libraries like `awilix` or `inversifyJS`, though you can also use simple `require` or `import` statements for basic uses.
