rollup-plugin-concat

1.0.4 verified Mon Apr 27 auth: no javascript maintenance

A Rollup plugin that concatenates files into single output files during the buildStart hook, making them available for import by other plugins. Version 1.0.4 is stable but has no recent updates (last release likely pre-2020). Key differentiator: integrates directly into Rollup's build pipeline with grouped file configurations. Alternative to manual concatenation or separate build steps.

Common errors

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

cause Package not installed or import path incorrect.

fix

Run: npm install rollup-plugin-concat --save-dev

error TypeError: concat is not a function ↓

cause Imported as named export instead of default.

fix

Use: import concat from 'rollup-plugin-concat'

error [!] (plugin concat) Error: groupedFiles must be an array ↓

cause Options object missing groupedFiles or not an array.

fix

Provide options as { groupedFiles: [ {...} ] }

Warnings

gotcha Plugin only runs on buildStart hook; output files are generated before subsequent plugins run, but are not watched for changes. ↓

fix Ensure that concatenated files are static or trigger a rebuild manually if they change.

gotcha Output file paths are relative to the current working directory, not relative to the Rollup config file. ↓

fix Use absolute paths or resolve relative to __dirname.

deprecated The package has not been updated in several years; may not work with Rollup 3+ due to hook changes. ↓

fix Consider using @rollup/plugin-multi-entry or manual concatenation scripts.

Install

npm install rollup-plugin-concat

yarn add rollup-plugin-concat

pnpm add rollup-plugin-concat

Imports

concat

wrong

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

correct

import concat from 'rollup-plugin-concat'

ESM-only; CommonJS require will fail unless project uses esModuleInterop.

default export

wrong

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

correct

import concat from 'rollup-plugin-concat'

The plugin exports a default function only.

Quickstart

Configures rollup-plugin-concat to concatenate fileA.js and fileB.js into ab.js before bundling.

import concat from 'rollup-plugin-concat';

export default {
  input: 'src/index.js',
  output: {
    file: 'bundle.js',
    format: 'esm'
  },
  plugins: [
    concat({
      groupedFiles: [
        {
          files: ['./fileA.js', './fileB.js'],
          outputFile: './ab.js'
        }
      ]
    })
  ]
};