Bundling your Web Components with vite

The aim of this section is to highlight some features we found useful to bundle Web Components together.

Let's say we have a bunch of Web Components such as

├── my-button
|   └── index.js
|   └── manifest.js
|
├── my-table
|   └── index.js
|   └── manifest.js
|
├── index.js
├── my-components.js
|

The most important thing to remember is that Web Component definitions must appear once and they must not repeat themself even accidentally (the bundler might mess up with the tree of dependencies).

Another point of attention must be the desired output: whether the library will be consumed by browsers only or could be made available to Node.js environments as development resource, say by publishing an npm library.

In the latter case you might consider having a library entrypoint my-components.js and an npm package entrypoint index.js

The components might look like

// my-button/index.js

export default class MyButton extends HTMLElement {
  static get __manifest() {
    return import('./manifest').then(({default: manifest}) => manifest)
  }

  /**
   * properties and lifecycle
   */
}

the browser entrypoint could be:

// my-components.js
import MyButton from './my-button'
import MyTable from './my-table'

window.customElements.define('my-button', MyButton)
window.customElements.define('my-table', MyTable)

and the npm index.js would look like:

import MyButton from './my-button'
import MyTable from './my-table'

export {
  MyButton,
  MyTable,
}

the vite configuration would produce the browser bundle being:

// vite.config.ts
import {defineConfig} from 'vite'

export default defineConfig({
  // rest of the configuration
  build: {
    // rest of build configuration
    rollupOptions: {
      input: {
        'my-components': '/path/to/my-components.js'
      }
    }
  }
})

the npm bundle can be instead obtained using tools like esbuild or tsc.

Bundling components separately is another strategy:

// vite.config.ts
import {defineConfig} from 'vite'

export default defineConfig({
  // rest of the configuration
  build: {
    // rest of build configuration
    rollupOptions: {
      input: {
        'my-button': '/path/to/my-button/index.js'
        'my-table': '/path/to/my-table/index.js'
      }
    }
  }
})

Be aware that runtime loading of Web Components is a key factor here. The browser window won't be able to follow dynamic imports in order to wait page onload event, which means that loading multiple Web Components from different bundles might make them appear at different times. A consistent visualization is instead guaranteed when the components are loaded together, at least to a further degree.

This remark does not rule out separate bundles. For instance micro-lc is bundled separately with respect to its loading Web Component, which by default shows spinning hexagons until micro-lc fires an onload event. mlc-loading-animation loads first and is safe to assume won't need micro-lc to be loaded to start its work.

A components library providing buttons, tables, forms, is definitively an example of a set of Web Components which must be bundled together:

1. they load together avoiding weird flashes
2. they reuse chunks of code like stylesheets