Use npm.umd.entry config to customise the UMD build entry point

Fixes #411

CHANGES.md

@@ -1,5 +1,9 @@
 # Unreleased (in `master`)
 
+## Added
+
+- Added [`npm.umd.entry` config](https://github.com/insin/nwb/blob/master/docs/Configuration.md#entry-string) to specify a different entry point for the UMD build in npm module projects. Currently, the UMD build requires an entry point which *must* have a `default` export [[#411](https://github.com/insin/nwb/issues/411)]
+
 ## Fixed
 
 - Always add `CopyPlugin` when [`webpack.copy` config](https://github.com/insin/nwb/blob/master/docs/Configuration.md#copy-array--object) is provided [[#431](https://github.com/insin/nwb/issues/431)]

docs/Configuration.md

@@ -120,6 +120,7 @@ The configuration object can include the following properties:
   - [`npm.esModules`](#esmodules-boolean) - toggle creation of an ES modules build
   - UMD build
     - [`npm.umd`](#umd-string--object--false) - configure a UMD build which exports a global variable
+      - [`umd.entry`](#entry-string) - use a different entry point for the UMD build
       - [`umd.global`](#global-string) - global variable name exported by UMD build
       - [`umd.externals`](#externals-object) - dependencies to use via global variables in UMD build
     - [`package.json` fields](#packagejson-umd-banner-configuration)
@@ -1127,6 +1128,33 @@ module.exports = {
 
 If you also have some external dependencies to configure, use an object containing the following properties:
 
+###### `entry`: `String`
+
+Specifies a module which will be the entry point for the UMD build. Otherwise the default entry (`src/index.js`) is used.
+
+Currently, the UMD entry point *must* have a `default` export, but you might want to have named exports from the default entry point for people using your module via npm, e.g. if you're publishing a component library.
+
+```js
+module.exports = {
+  npm: {
+    umd: {
+      global: 'MyComponentLibrary',
+      entry: './umd.js',
+      externals: {
+        'react': 'React'
+      }
+    }
+  }
+}
+```
+
+In this scenario, `umd.js` could `import *` a module which uses named exports and re-export its contents as `default`:
+
+```js
+import * as components from './src/index.js`
+export default components
+```
+
 ###### `global`: `String`
 
 The name of the global variable the UMD build will export.

src/config/npm.js

@@ -61,6 +61,7 @@ export function processNpmBuildConfig({report, userConfig}) {
     }
     else {
       let {
+        entry,
         global: umdGlobal,
         externals,
         ...unexpectedConfig
@@ -76,6 +77,14 @@ export function processNpmBuildConfig({report, userConfig}) {
         )
       }
 
+      if ('entry' in umd && typeOf(entry) !== 'string') {
+        report.error(
+          'npm.umd.entry',
+          entry,
+          `Must be a ${chalk.cyan('String')}`
+        )
+      }
+
       if ('global' in umd && typeOf(umdGlobal) !== 'string') {
         report.error(
           'npm.umd.global',

src/moduleBuild.js

@@ -69,7 +69,7 @@ function buildUMD(args, buildConfig, userConfig, cb) {
   let entry = path.resolve(args._[1] || 'src/index.js')
   let webpackBuildConfig = {
     babel: buildConfig.babel,
-    entry: [entry],
+    entry: [userConfig.npm.umd.entry || entry],
     output: {
       filename: `${pkg.name}.js`,
       library: userConfig.npm.umd.global,

tests/config-test.js

@@ -83,6 +83,30 @@ describe('processUserConfig()', () => {
     it('babel.runtime is not valid', () => {
       check({babel: {runtime: 'welp'}}, 'babel.runtime', /Must be/)
     })
+    it('npm contains unexpected prop', () => {
+      check({npm: {invalid: true}}, 'npm', /Unexpected prop/)
+    })
+    it('npm.cjs is an invalid type', () => {
+      check({npm: {cjs: 'yes'}}, 'npm.cjs', /Must be/)
+    })
+    it('npm.esModules is an invalid type', () => {
+      check({npm: {esModules: 'no'}}, 'npm.esModules', /Must be/)
+    })
+    it('npm.umd is an invalid type', () => {
+      check({npm: {umd: /invalid/}}, 'npm.umd', /Must be/)
+    })
+    it('npm.umd contains unexpected prop', () => {
+      check({npm: {umd: {invalid: true}}}, 'npm.umd', /Unexpected prop/)
+    })
+    it('npm.umd.entry is an invalid type', () => {
+      check({npm: {umd: {entry: /invalid/}}}, 'npm.umd.entry', /Must be/)
+    })
+    it('npm.umd.global is an invalid type', () => {
+      check({npm: {umd: {global: /invalid/}}}, 'npm.umd.global', /Must be/)
+    })
+    it('npm.umd.externals is an invalid type', () => {
+      check({npm: {umd: {externals: /invalid/}}}, 'npm.umd.externals', /Must be/)
+    })
     it('webpack contains unexpected prop', () => {
       check({webpack: {invalid: true}}, 'webpack', /Unexpected prop/)
     })