Bundling a plugin with Rollup but having duplicate Vue.js package imported in the client app's bundle (Nuxt)

Question

Dear Stack Overflow / Vue.js / Rollup community

This could be a noob question for the master plugin developers working with Vue and Rollup. I will write the question very explicitly hoping that it could help other noobs like me in the future.

I have simple plugin that helps with form validation. One of the components in this plugin imports Vue in order to programatically create a component and append to DOM on mount like below:

import Vue from 'vue'
import Notification from './Notification.vue' /* a very simple Vue component */
...
mounted() {
  const NotificationClass = Vue.extend(Notification)
  const notificationInstance = new NotificationClass({ propsData: { name: 'ABC' } })
  notificationInstance.$mount('#something')
}

This works as expected, and this plugin is bundled using Rollup with a config like this:

import vue from 'rollup-plugin-vue'
import babel from 'rollup-plugin-babel'
import { terser } from 'rollup-plugin-terser'
import resolve from 'rollup-plugin-node-resolve'
import commonjs from 'rollup-plugin-commonjs'

export default {
  input: 'src/index.js',
  output: {
    name: 'forms',
    globals: {
      vue: 'Vue'
    }
  },
  plugins: [
    vue(),
    babel(),
    resolve(),
    commonjs(),
    terser()
  ],
  external: ['vue']
}

As you can see, Vue.js is getting externalised in this bundle. The aim (and the assumption) is that the client app that imports this plugin will be running on Vue, therefore there's no need to bundle it here (assumption).

The very simple src/index.js that the bundler uses is below:

import Form from './Form.vue'

export default {
  install(Vue, _) {
    Vue.component('bs-form', Form)
  }
}

Rollup creates 2 files (one esm and one umd) and references them in in the plugins package.json file like below:

  "name": "bs-forms",
  "main": "./dist/umd.js",
  "module": "./dist/esm.js",
  "files": [
    "dist/*"
  ],
  "scripts": {
    "build": "npm run build:umd & npm run build:es",
    "build:es": "rollup --config rollup.config.js --format es --file dist/esm.js",
    "build:umd": "rollup --config rollup.config.js --format umd --file dist/umd.js"
  }

Everything works as expected up to this point and the bundles are generated nicely.

The client app (Nuxt SSR) imports this plugin (using npm-link since it's in development) with a very simple import in a plugin file:

/* main.js*/
import Vue from 'vue'

import bsForms from 'bs-forms'
Vue.use(bsForms)

This plugin file (main.js) is added to nuxt.config.js as a plugin:

// Nuxt Plugins
...
plugins: [{src: '~/plugins/main'}]
...

Everything still works as expected but here comes the problem:

Since the clients is a Nuxt app, the Vue is imported by default of course but the externalised Vue module (by the forms plugin) is also imported in the client. Therefore there is a duplication of this package in the client bundle.

I guess the client app can configure its webpack config in order to remove this duplicated module. Perhaps by using something like a Dedupe plugin or something? Can someone suggests how to best handle situation like these?

But what I really want to learn, is the best practice of bundling the plugin at the first place, so that the client doesn't have to change anything in its config and simply imports this plugin and move on.

I know that importing the Vue.js in the plugin may not be a great thing to do at the first place. But there could be other reasons for an import like this as well, for example imagine that the plugin could be written in Typescript and Vue.js / Typescript is written by using Vue.extend statements (see below) which also imports Vue (in order to enable type interface):

import Vue from 'vue'

const Component = Vue.extend({
  // type inference enabled
})

So here's the long question. Please masters of Rollup, help me and the community out by suggesting best practice approaches (or your approaches) to handle situations like these.

Thank you!!!!

Answer 1

I have sorted this problem with an interesting caveat:

The duplicate Vue package doesn't get imported when the plugin is used via an NPM package (installed by npm install -save <plugin-name> )

However, during development, if you use the package vie npm link (like npm link <plugin-name>) then Vue gets imported twice, like shown in that image in the original question.

People who encounter similar problems in the future, please try to publish and import your package and see if it makes any difference.

Thank you!