How to do Dependency Injection in RequireJS?

example_code.js

define([], function () {

    return function HypotheticalHelperMethod() {
        doSomeOtherStuff();
    }

});


define(["helperMethod"], function (helperMethod) {

   MyClass = function () {
        this.init()
   }

   MyClass.prototype.init = function () {

        helperMethod(1, 2, 3);

   }

});

example_test.js

require(["helperMethod", "myClass"], function (helperMethod, myClass) {

    describe("MyClass tests", function () {

        it("calls `helperMethod` upon init", function () {

            // here i need to spyOn helperMethod, but if I set helperMethod
            // to a jasmime spy:
            helperMethod = jasmine.createSpy("helperMethod");
            // I've altered my reference, and MyClass still has the original
            // HypotheticalHelperMethod function.

            var instance = new MyClass();

            expect(helperMethod).toHaveBeenCalledWith(1, 2, 3);

        });

    });

});

Ah, OK. If you want to just cram in a modification after a module has been created but before listeners are given a reference to it, you can use the semi-private onResourceLoad API:

https://github.com/jrburke/requirejs/wiki/Internal-API:-onResourceLoad

Note this API is always subject to change. It has been stable for a while, but no guarantees for the future, even though I have no immediate plans to change it.

To modify the value passed to modules dependent on the current module, this would work:

requirejs.onResourceLoad = function (context, map, depArray) {
  var id = map.id,
    internalModule = context.registry[id],
    existingExport = context.defined[id];

    //modify existing export here

    //If the modification is a modification to the base export (like
    //if the export was a function) and not just a property
    //modification on the export, hard set the new module value:
    internalModule.exports = context.defined[id] = newExportValue;
};

This onResourceLoad definition should be done after require.js loads, but before any module loading is done, at least for modules that you want to intercept.

@keithamus did you find a way to test that your helperMethod is called?