feat: allow external dependencies to be mapped to a specific file

Closes #66

README.md

@@ -63,6 +63,31 @@ commonjsPreprocessor: {
 ```
 When not specified the root folder defaults to the `karma.basePath/node_modules` configuration option.
 
+#### Externals
+
+When external dependencies have prebundled sources.
+You can specify what file should be included from the root folder
+
+```js
+// karma.conf.js
+module.exports = function(config) {
+  config.set({
+    // ...
+    commonjsPreprocessor: {
+      modulesRoot: 'components',
+      externals: {
+        'angular': 'angular/angular.min.js'
+      }
+    },
+    // ...
+  });
+};
+```
+
+This effectively translates any `require('angular')` statements into `require('./components/angular/angular.min.js')`.
+
+----
+
 For an example project, check out Karma's [client tests](https://github.com/karma-runner/karma/tree/master/test/client).
 
 ----

lib/plugin.js

@@ -3,7 +3,28 @@ var os = require('os');
 
 var BRIDGE_FILE_PATH = path.normalize(__dirname + '/../client/commonjs_bridge.js');
 
-var initCommonJS = function(/* config.files */ files) {
+var initCommonJS = function(
+  files,
+  config,
+  basePath,
+  preprocessors,
+) {
+
+  if (config.externals) {
+    const keys = Object.keys(config.externals);
+    for (const key of keys) {
+      const pattern = path.resolve(config.modulesRoot || 'node_modules', config.externals[key]);
+      console.log(pattern);
+      files.push({
+        pattern: pattern,
+        included: true,
+        served: true,
+        watched: false,
+      });
+      preprocessors[pattern] = preprocessors[pattern] || [];
+      preprocessors[pattern].push("commonjs");
+    }
+  }
 
   // Include the file that resolves all the dependencies on the client.
   files.push({
@@ -13,6 +34,12 @@ var initCommonJS = function(/* config.files */ files) {
     watched: false
   });
 };
+initCommonJS.$inject = [
+  "config.files",
+  "config.commonjsPreprocessor",
+  "config.basePath",
+  "config.preprocessors",
+];
 
 var createPreprocesor = function(logger, config, basePath) {
   var log = logger.create('preprocessor.commonjs');
@@ -24,6 +51,17 @@ var createPreprocesor = function(logger, config, basePath) {
 
   log.debug('Configured root path for modules "%s".', modulesRootPath);
 
+  const externalAugment = {};
+  if (config.externals) {
+    const keys = Object.keys(config.externals);
+
+    for (const key of keys) {
+      const expectedPath = path.resolve(modulesRootPath, key, "index.js");
+      const actualPath = path.resolve(modulesRootPath, config.externals[key]);
+      externalAugment[actualPath] = expectedPath;
+    }
+  }
+
   return function(content, file, done) {
 
     if (file.originalPath === BRIDGE_FILE_PATH) {
@@ -32,6 +70,10 @@ var createPreprocesor = function(logger, config, basePath) {
 
     log.debug('Processing "%s".', file.originalPath);
 
+    if (externalAugment[file.path]) {
+      file.path = externalAugment[file.path];
+    }
+
     if (path.extname(file.originalPath) === '.json') {
       return done('window.__cjs_module__["' + file.path + '"] = ' + content + ';' + os.EOL);
     }