Entry Chunk

An entry chunk is created, because we need to output a JavaScript file for:

• Exporting the exports of the entry module
• Representing the executing point of the corresponding entry.
• Storing the code of the entry module and its dependencies (if not code-split into separate chunks)

Let's say you have an app that could run separately but also could be used as a library by other apps.

File structure:

// component.js
export function component() {
  return 'Hello World';
}

// render.js
export function render(component) {
  console.log(component());
}

// app.js
import { component } from './component.js';
import { render } from './render.js';

render(component);

// lib.js
export { component } from './component.js';

Config:

export default defineConfig({
  input: {
    app: './app.js',
    lib: './lib.js',
  },
});

Rolldown will create outputs like:

app.js

import { component } from './common.js';

function render(component) {
  console.log(component());
}

render(component);

lib.js

export { component } from './common.js';

common.js

export function component() {
  return 'Hello World';
}

• lib.js is created because we need to create the export signature export { component } and export it in lib.js.
• For app.js, though it doesn't export anything, we still need to create app.js as the executing point of the app.
• You'll also notice, from the executing point app.js, only modules, like render.js, imported are executed. This is another reason and promise made by being the executing point.