add the possibility to intercept require() calls

[jankuca]

These two functions make it possible to inject mock modules required after the host module is loaded.

If for instance a module has a method which requires another module in its logic, it is possible to inject the mock there:

// x.js:
exports.getModule = function () {
    return require("abc");
};

Even though the require call occurs after the module load, we can alter the results:

var theModule = require('./x.js');
theModule.__setRequiredModule__("abc", abc);
assert(theModule.getModule() === abc);

[jhnns]

First of all: thanks for your effort! You even included tests 👍

Unfortunately I'm not quite convinced. I understand your motivation because you'd like to simply swap the required module with a mock, but your solution will only work if the dependency is required after the module has been initialized. But most of the time - and I even consider it to be best practice - dependencies are required on initialization.

One thing I like about the way rewire works is that dependencies are resolved as usual and swapped after initialization which reveals errors like "module cannot be resolved". But this approach of course implies that all require() calls are done in the top-level scope of the module and that no logic is executed on module initialization.

I discussed this topic some months ago in this issue.

However, I do think that it's possible to swap the module's dependencies on initialization since rewire has access to the private scope of the module and thus can override the require()-function. The api could look like:

var myModule = rewire("./myModule", {
    "fs": fsMock,
    "../other/module.js": otherModuleMock
});

Need to think about it. Any thoughts anyone? 😁

[sokra]

@jhnns You can use sandboxed-module with a rewire sourceTransformers.

[jhnns]

Thx, but I know sandboxed-module. One key feature of rewire is that it doesn't use vm and is trying to emulate node's module environment. Instead of that it uses node's internal module-module to compile the rewired module, so everything is as if it would be required conventionally.

[jankuca]

Um, nevermind.

I was using the added methods for mocking of JSON files loaded via require() but I replaced this with mock-fs and it works flawlessly.

Feel free to merge this later if you find it useful but I do not need the feature anymore. Cheers!

[jhnns]

Yep, mock-fs is probably the better choice for your use-case. Anyway, thanks! 😄