Calling a variable which is a function without passing parameters to it

Question

If you look at this line https://github.com/hapijs/hapi-auth-basic/blob/master/lib/index.js#L14 , you can see that it calls internals.implementation without passing in any parameters, but the method has 2 parameters https://github.com/hapijs/hapi-auth-basic/blob/master/lib/index.js#L14 .

How does the method internals.implementation work if no params are passed into it?

Answer 1

On line 14, internals.implementation is not actually being called. Rather, a reference to the function is being passed to plugins.auth.scheme() , presumably to be invoked later by the auth plugin (where actual parameters will be passed).

For example, here's a simplified version:

 function sampleImplementation(message) { alert(message); } function useImplementation(implementation, message) { implementation.apply(this, [message]); // invoke the function with args } useImplementation(sampleImplementation, "hey there!"); // should alert "hey there!"