What is the best way to pass common variables into separate modules in Node.js?

Question

I use separate router files as modules for main app and auth app. I can\'t get the best way to pass variables(db client) into routers. I don\'t want to hardcode it or pass i

Answer 1

You can save yourself all the boilerplate code of wiring up your modules if you use a dependency injection framework

This answer lists a few of them. I also built a simpler DI framework here.

EDIT: below is a copy form the answer in case that page changes

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require is the way of managing dependencies in Node.js and surely it is intuitive and effective, but it has also its limitations.

My advice is to take a look at some of the Dependency Injection containers available today for Node.js to have an idea on what are their pros/cons. Some of them are:

• Scatter
• Electrolyte
• Wire
• Intravenous
• Pongular

Just to name a few.

Now the real question is, what can you achieve with a Node.js DI container, compared to a simple require?

Pros:

• better testability: modules accepts their dependencies as input
• Inversion of Control: decide how to wire your modules without touching the main code of your application.
• a customizable algorithm for resolving modules: dependencies have "virtual" identifiers, usually they are not bound to a path on the filesystem.
• Better extensibility: enabled by IoC and "virtual" identifiers.
• Other fancy stuff possible:
  • Async initialization
  • Module lifecycle management
  • Extensibility of the DI container itself
  • Can easily implement higher level abstractions (e.g. AOP)

Cons:

• Different from the Node.js "experience": not using require definitely feels like you are deviating from the Node way of thinking.
• The relationship between a dependency and its implementation is not always explicit. A dependency may be resolved at runtime and influenced by various parameters. The code becomes more difficult to understand and debug
• Slower startup time
• Maturity (at the moment): none of the current solutions is really popular at the moment, so not so many tutorials, no ecosystem, not battle tested.
• Some DI containers will not play well with module bundlers like Browserify and Webpack.