What Path is the Babel Plugin module-alias Actually Using? - babeljs

Question

I'm trying to use Babel's "module-alias" plug-in with the "proxyquire" testing library, but I'm not having a lot of luck.
Library Backstory
(feel free to skip if you are familiar with both module-alias/proxyquire)
Proxyquire let's you mock out a module's dependencies for testing, like so:
const someFunctionToTest =
proxyquire(pathToSomeFunctionToTestsModule, {
pathToDependency: fakeVersionOfDependency
});
Babel's module-alias plugin let's you make your import paths more convenient and consistent. For instance, I can specify (in .babelrc):
"plugins": [
["module-alias", [
{ "src": "./", "expose": "~" }
]],
and then instead of having to type (when importing from a module nested three directories deep) require('../../../someModule') I can just typerequire('~/someModule')`.
The Problem
My problem is, they don't work together. If I havesomeModule that depends on someDependency:
// src/someModule.js
const someDependency = require('~/src/someDependency');
doSomethingWith(someDependency);
and then I want to test someModule with a mock version of someDependency, I should be able to do:
const proxiedSomeModule =
proxyquire('~/src/someModule', {
'~/src/someDependency': fakeVersionOfSomeDependency
});
... but proxyquire tells me `Error: Cannot find module '~/src/someModule'.
Presumably ("behind the scenes") Babel is converting '~/src/someModule' into its real path, so when Proxyquire looks for the aliased path it can't find it.
The Question
My question is: is there any way I can find out what the real path of '~/src/someModule' is, after Babel converts it (ie. when proxyquire deals with it)? Or alternatively is there any way to get proxyquire to just work with the aliased paths?

Answer 1

It turns out the "real" path (for '~/someModule') generated by module resolver is just the ../../someModule path. However, it also turns out that there is no need to convert paths by hand.
The module resolver plug-in will convert the arguments to any functions on its transformFunctions list. This means that you can convert any string to its non-aliased form by doing the following:
Define a simple passthrough function, e.g. const resolveModulePath = path => path;
Add that function (along with proxyquire) to the transformFunctions list in .babelrc:
["module-resolver", {
"transformFunctions": ["proxyquire", "resolveModulePath"]
}]
Wrap any paths which aren't arguments to a function with resolveModulePath:
proxyquire('~/some/path/someModule', {
[resolveModulePath('~/some/other/path')]: {
someFunction: fakeSomeFunction
}
})
Note that the first path in the above doesn't need to be escaped, as its an argument to a transformed function. Only the second path ('~/some/other/path') needs to be wrapped, because it's part of an object which is an argument; the string itself isn't an argument, until it's wrapped.
For further info see: https://github.com/tleunen/babel-plugin-module-resolver/issues/241#issuecomment-350109168