minor: add option to specify additional entries

Author: chrisbreiding

README.md

@@ -48,6 +48,7 @@ Pass in options as the second argument to `webpack`:
 
 ```javascript
 const webpack = require('@cypress/webpack-preprocessor')
+
 module.exports = (on) => {
   const options = {
     // send in the options from your webpack.config.js, so it works the same
@@ -93,6 +94,29 @@ Object of options for watching. See [webpack's docs](https://webpack.github.io/d
 
 **Default**: `{}`
 
+### additionalEntries
+
+An array of file path strings for additional entries to be included in the bundle.
+
+By necessity, this preprocessor sets the entry point for webpack as the spec file or support file. The `additionalEntries` option allows you to specify more entry points in order to utilize webpack's [multi-main entry](https://webpack.js.org/concepts/entry-points/#single-entry-shorthand-syntax). This allows runtime dependency resolution.
+
+**Default**: `[]`
+
+**Example**:
+
+```javascript
+const webpack = require('@cypress/webpack-preprocessor')
+
+module.exports = (on) => {
+  const options = {
+    webpackOptions: require('../../webpack.config'),
+    additionalEntries: ['./app/some-module.js'],
+  }
+
+  on('file:preprocessor', webpack(options))
+}
+```
+
 ## Modifying default options
 
 The default options are provided as `webpack.defaultOptions` so they can be more easily modified.

index.js

@@ -72,14 +72,15 @@ const preprocessor = (options = {}) => {
     debug('webpackOptions: %o', webpackOptions)
     debug('watchOptions: %o', watchOptions)
 
+    const entry = [filePath].concat(options.additionalEntries || [])
     // we're provided a default output path that lives alongside Cypress's
     // app data files so we don't have to worry about where to put the bundled
     // file on disk
     const outputPath = file.outputPath
 
     // we need to set entry and output
     webpackOptions = Object.assign(webpackOptions, {
-      entry: filePath,
+      entry,
       output: {
         path: path.dirname(outputPath),
         filename: path.basename(outputPath),

test/index_spec.js

@@ -98,7 +98,19 @@ describe('webpack preprocessor', function () {
 
       it('specifies the entry file', function () {
         return this.run().then(() => {
-          expect(webpack.lastCall.args[0].entry).to.equal(this.file.filePath)
+          expect(webpack.lastCall.args[0].entry).to.eql([this.file.filePath])
+        })
+      })
+
+      it('includes additional entry files', function () {
+        return this.run({
+          additionalEntries: ['entry-1.js', 'entry-2.js'],
+        }).then(() => {
+          expect(webpack.lastCall.args[0].entry).to.eql([
+            this.file.filePath,
+            'entry-1.js',
+            'entry-2.js',
+          ])
         })
       })