Idiomatic Javascript dependency graph

Question

Given the following Javascript, would it be better/more idiomatic to inject the MyService object into myMethod so that a fake version of MyService could be injected for testing? Or am I missing something?

var myObject = {
  myMethod: function() {
    var myService = new MyService();
    return myService.doSomething();
  }
}

Milad Naseri · Accepted Answer · 2012-01-18 12:00:07Z

1

Dependency injection always takes precedence over hard-coding the dependencies. Also, by coding to interfaces (assuming the myObject instance has been given a copy of a Service object that has a doSomething() method) could come handy here.

answered Jan 18, 2012 at 12:00

Milad Naseri

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3 Comments

Ben Aston Over a year ago

By "interface" I presume you mean that the prototype of MyService is set to Service? Given that methods can be changed dynamically in JS, what are the benefits of this approach over and above simply re-defining (say) doSomething in my test?

Milad Naseri Over a year ago

Exactly. It has no performance gains. It only makes your program more readable by allowing the reader to understand the contract (interface) and then follow the logic inside the implementation.

Milad Naseri Over a year ago

No problem. I hope I've been able to help you.

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