rollup-plugin-hypothetical

2.1.1 verified Mon Apr 27 auth: no javascript

A Rollup plugin that provides a virtual file system for testing other plugins without actual disk I/O. Version 2.1.1 is stable, with infrequent releases. Unlike other virtual file plugins, it supports sourcemaps via { code, map } objects, configurable fallthrough behavior, implied extensions, and custom CWD. Ideal for unit testing Rollup plugins that depend on file resolution.

Common errors

error Error: Could not resolve './nonexistent.js' from 'main.js' ↓

cause File not defined in options.files and allowFallthrough is false.

fix

Add the file to options.files or set allowFallthrough: true if you want Rollup to resolve it from disk.

error Error: Cannot find module 'rollup-plugin-hypothetical' ↓

cause Package not installed.

fix

Run npm install --save-dev rollup-plugin-hypothetical.

error TypeError: hypothetical is not a function ↓

cause Incorrect import: using named import instead of default.

fix

Use import hypothetical from 'rollup-plugin-hypothetical' (default import).

Warnings

gotcha Options.files keys are resolved relative to process.cwd() by default, not rollup's input file directory. ↓

fix Use absolute paths or set options.cwd explicitly to match your project root.

deprecated Using options.files with a plain object may cause issues with keys like __proto__. ↓

fix Use options.filesMap (Map) instead to avoid prototype pollution.

gotcha External imports fall through by default (allowExternalFallthrough=true), which may cause silent errors if the import is not resolved. ↓

fix Set allowExternalFallthrough: false to force explicit definitions for external imports.

breaking options.impliedExtensions default changed from ['.js'] to ['.js', '/'] in v2.0.0. ↓

fix If relying on the old default, explicitly set impliedExtensions: ['.js'].

Install

npm install rollup-plugin-hypothetical

yarn add rollup-plugin-hypothetical

pnpm add rollup-plugin-hypothetical

Imports

default

wrong

const hypothetical = require('rollup-plugin-hypothetical').default

correct

import hypothetical from 'rollup-plugin-hypothetical'

ESM-only; has default export.

hypothetical

wrong

import { hypothetical } from 'rollup-plugin-hypothetical'

correct

import hypothetical from 'rollup-plugin-hypothetical'

Export is default, not named.

hypothetical

wrong

const { hypothetical } = require('rollup-plugin-hypothetical')

correct

const hypothetical = require('rollup-plugin-hypothetical')

CJS require returns the default; destructuring fails.

Quickstart

Creates a Rollup config with hypothetical files for a simple greeting module.

// rollup.config.js
import hypothetical from 'rollup-plugin-hypothetical';

export default {
  input: 'main.js',
  plugins: [
    hypothetical({
      files: {
        'main.js': `
          import { greet } from './greet.js';
          console.log(greet('World'));
        `,
        'greet.js': `
          export function greet(name) {
            return 'Hello, ' + name + '!';
          }
        `
      }
    })
  ],
  output: { file: 'out.js', format: 'esm' }
};

// Then run: npx rollup -c