feat(build): support named exports when building --target lib with js/ts entry

close #1436

BREAKING CHANGE: When building a js/ts entry file with --target lib, the
library now exposes a Module with both default and named exports. This means
in the UMD build, the default export now needs to be accessed as
`window.yourLib.default`, and in the CommonJS build as
`const yourLib = require('yourLib').default`. If you don't have named exports
and want to retain the previous behavior, you can configure webpack to use
`output.libraryExport: 'default'` in `vue.config.js`.

packages/@vue/cli-service/__tests__/buildLib.spec.js

@@ -1,4 +1,4 @@
-jest.setTimeout(30000)
+jest.setTimeout(40000)
 
 const path = require('path')
 const portfinder = require('portfinder')
@@ -8,6 +8,12 @@ const create = require('@vue/cli-test-utils/createTestProject')
 const launchPuppeteer = require('@vue/cli-test-utils/launchPuppeteer')
 
 let server, browser, page
+
+afterEach(async () => {
+  await browser.close()
+  server.close()
+})
+
 test('build as lib', async () => {
   const project = await create('build-lib', defaultPreset)
 
@@ -45,7 +51,40 @@ test('build as lib', async () => {
   expect(h3Text).toMatch('Installed CLI Plugins')
 })
 
-afterAll(async () => {
-  await browser.close()
-  server.close()
+test('build as lib (js)', async () => {
+  const project = await create('build-lib-js', defaultPreset)
+  await project.write('src/main.js', `
+    export default { foo: 1 }
+    export const bar = 2
+  `)
+  const { stdout } = await project.run('vue-cli-service build --target lib --name testLib src/main.js')
+  expect(stdout).toMatch('Build complete.')
+
+  expect(project.has('dist/demo.html')).toBe(true)
+  expect(project.has('dist/testLib.common.js')).toBe(true)
+  expect(project.has('dist/testLib.umd.js')).toBe(true)
+  expect(project.has('dist/testLib.umd.min.js')).toBe(true)
+
+  const port = await portfinder.getPortPromise()
+  server = createServer({ root: path.join(project.dir, 'dist') })
+
+  await new Promise((resolve, reject) => {
+    server.listen(port, err => {
+      if (err) return reject(err)
+      resolve()
+    })
+  })
+
+  const launched = await launchPuppeteer(`http://localhost:${port}/demo.html`)
+  browser = launched.browser
+  page = launched.page
+
+  // should expose a module with default and named exports
+  expect(await page.evaluate(() => {
+    return window.testLib.default.foo
+  })).toBe(1)
+
+  expect(await page.evaluate(() => {
+    return window.testLib.bar
+  })).toBe(2)
 })

packages/@vue/cli-service/lib/commands/build/demo-lib-js.html

@@ -0,0 +1,7 @@
+<title><%- htmlWebpackPlugin.options.libName %> demo</title>
+<script src="./<%- htmlWebpackPlugin.options.libName %>.umd.js"></script>
+<link rel="stylesheet" href="./<%- htmlWebpackPlugin.options.libName %>.css">
+
+<script>
+console.log(<%- htmlWebpackPlugin.options.libName %>)
+</script>

packages/@vue/cli-service/lib/commands/build/resolveLibConfig.js

@@ -21,6 +21,7 @@ module.exports = (api, { entry, name }, options) => {
     )
   }
 
+  const isVueEntry = /\.vue$/.test(entry)
   const libName = (
     name ||
     api.service.pkg.name ||
@@ -57,10 +58,11 @@ module.exports = (api, { entry, name }, options) => {
 
     // inject demo page for umd
     if (genHTML) {
+      const template = isVueEntry ? 'demo-lib.html' : 'demo-lib-js.html'
       config
         .plugin('demo-html')
           .use(require('html-webpack-plugin'), [{
-            template: path.resolve(__dirname, './demo-lib.html'),
+            template: path.resolve(__dirname, template),
             inject: false,
             filename: 'demo.html',
             libName
@@ -80,21 +82,22 @@ module.exports = (api, { entry, name }, options) => {
       [entryName]: require.resolve('./entry-lib.js')
     }
 
-    Object.assign(rawConfig.output, {
-      filename: `${entryName}.js`,
-      chunkFilename: `${entryName}.[name].js`,
+    rawConfig.output = Object.assign({
       library: libName,
-      libraryExport: 'default',
+      libraryExport: isVueEntry ? 'default' : undefined,
       libraryTarget: format,
-      // use dynamic publicPath so this can be deployed anywhere
-      // the actual path will be determined at runtime by checking
-      // document.currentScript.src.
-      publicPath: '',
       // preserve UDM header from webpack 3 until webpack provides either
       // libraryTarget: 'esm' or target: 'universal'
       // https://github.com/webpack/webpack/issues/6522
       // https://github.com/webpack/webpack/issues/6525
       globalObject: `typeof self !== 'undefined' ? self : this`
+    }, rawConfig.output, {
+      filename: `${entryName}.js`,
+      chunkFilename: `${entryName}.[name].js`,
+      // use dynamic publicPath so this can be deployed anywhere
+      // the actual path will be determined at runtime by checking
+      // document.currentScript.src.
+      publicPath: ''
     })
 
     return rawConfig