rollup-plugin-by-output

1.0.1 verified Mon Apr 27 auth: no javascript

A Rollup plugin (or plugin helper) that allows applying Rollup plugins conditionally based on output options (format, file, etc.). Version 1.0.1 is the latest stable release. It helps reduce duplicate config when Rollup has multiple outputs that need different plugins (e.g., minification only for UMD builds). Key differentiator: provides elegant helpers like `when`, `whenAll`, `prop`, `format`, and `file` to filter plugins per output. Unlike manual array configs, it keeps code DRY. Requires Node >=8.3.0.

Common errors

error TypeError: plugins is not a function ↓

cause Using default import as an array or passing incorrect arguments to 'plugins'.

fix

Call plugins() with arguments: plugins(pluginA, [filter, pluginB]). Do not wrap in array brackets.

error when is not a function ↓

cause Importing 'when' incorrectly (e.g., import { when } from 'rollup-plugin-by-output' but package doesn't export it as named in CJS).

fix

Ensure your bundler supports ESM or use import { when } from 'rollup-plugin-by-output' with ES modules; in CJS, use const { when } = require('rollup-plugin-by-output').

error Module not found: Error: Can't resolve 'rollup-plugin-by-output' ↓

cause Package not installed or missing in node_modules.

fix

Run npm install --save-dev rollup-plugin-by-output

Warnings

gotcha The 'file' helper compares exact string equality, not a suffix. To match by file extension, use a custom function. ↓

fix Use when(file.name => name.endsWith('.min.js'), plugin) or prop('file', f => f.endsWith('.min.js'))

deprecated The package exports using default export for 'plugins' but named exports for helpers – mixing can cause confusion. ↓

fix Be explicit: import plugins, { when } from 'rollup-plugin-by-output'

Install

npm install rollup-plugin-by-output

yarn add rollup-plugin-by-output

pnpm add rollup-plugin-by-output

Imports

plugins

wrong

const plugins = require('rollup-plugin-by-output')

correct

import plugins from 'rollup-plugin-by-output'

ESM default import; CJS require works but not recommended for Rollup configs

when

wrong

const { when } = require('rollup-plugin-by-output')

correct

import { when } from 'rollup-plugin-by-output'

Named export; also available via CJS destructuring

file
```
import { file } from 'rollup-plugin-by-output'
```
Named export; commonly used to filter by output file path
format
```
import { format } from 'rollup-plugin-by-output'
```
Named export; commonly used to filter by output format (e.g., 'umd', 'cjs')

Quickstart

Applies babel to all outputs and terser only to the minified output.

import babel from 'rollup-plugin-babel';
import terser from 'rollup-plugin-terser';
import plugins, { file } from 'rollup-plugin-by-output';

export default {
  input: 'src/index.js',
  output: [
    { file: 'dist/bundle.js', format: 'cjs' },
    { file: 'dist/bundle.min.js', format: 'cjs' },
  ],
  plugins: plugins(
    babel(),
    [file('dist/bundle.min.js'), terser()]
  )
};