Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.
Learn more about Collectives
Teams
Q&A for work
Connect and share knowledge within a single location that is structured and easy to search.
Learn more about Teams
Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema

Ask Question
I have this simple helloworld react app created from an online course, however I get this error:
Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema. - configuration has an unknown property 'postcss'. These properties are valid: object { amd?, bail?, cache?, context?, dependencies?, devServer?, devtool?, entry, externals?, loader?, module?, name?, node?, output?, performance?, plugins?, profile?, recordsInputPath?, recordsO utputPath?, recordsPath?, resolve?, resolveLoader?, stats?, target?, watch?, watchOptions? } For typos: please correct them.
For loader options: webpack 2 no longer allows custom properties in configuration. Loaders should be updated to allow passing options via loader options in module.rules. Until loaders are updated one can use the LoaderOptionsPlugin to pass these options to the loader: plugins: [ new webpack.LoaderOptionsPlugin({ // test: /.xxx$/, // may apply this only for some modules options: { postcss: ... - configuration.resolve has an unknown property 'root'. These properties are valid: object { alias?, aliasFields?, cachePredicate?, descriptionFiles?, enforceExtension?, enforceModuleExtension?, extensions?, fileSystem?, mainFields?, mainFiles?, moduleExtensions?, modules?, plugins ?, resolver?, symlinks?, unsafeCache?, useSyncFileSystemCalls? } - configuration.resolve.extensions[0] should not be empty.
My webpack file is:
// work with all paths in a cross-platform manner
const path = require('path');
// plugins covered below
const { ProvidePlugin } = require('webpack');
const CopyWebpackPlugin = require('copy-webpack-plugin');
const HtmlWebpackPlugin = require('html-webpack-plugin');
// configure source and distribution folder paths
const srcFolder = 'src';
const distFolder = 'dist';
// merge the common configuration with the environment specific configuration
module.exports = {
    // entry point for application
    entry: {
        'app': path.join(__dirname, srcFolder, 'ts', 'app.tsx')
    // allows us to require modules using
    // import { someExport } from './my-module';
    // instead of
    // import { someExport } from './my-module.ts';
    // with the extensions in the list, the extension can be omitted from the 
    // import from path
    resolve: {
        // order matters, resolves left to right
        extensions: ['', '.js', '.ts', '.tsx', '.json'],
        // root is an absolute path to the folder containing our application 
        // modules
        root: path.join(__dirname, srcFolder, 'ts')
    module: {
        loaders: [
            // process all TypeScript files (ts and tsx) through the TypeScript 
            // preprocessor
            { test: /\.tsx?$/,loader: 'ts-loader' },
            // processes JSON files, useful for config files and mock data
            { test: /\.json$/, loader: 'json' },
            // transpiles global SCSS stylesheets
            // loader order is executed right to left
                test: /\.scss$/,
                exclude: [path.join(__dirname, srcFolder, 'ts')],
                loaders: ['style', 'css', 'postcss', 'sass']
            // process Bootstrap SCSS files
                test: /\.scss$/,
                exclude: [path.join(__dirname, srcFolder, 'scss')],
                loaders: ['raw', 'sass']
    // configuration for the postcss loader which modifies CSS after
    // processing
    // autoprefixer plugin for postcss adds vendor specific prefixing for
    // non-standard or experimental css properties
    postcss: [ require('autoprefixer') ],
    plugins: [
        // provides Promise and fetch API for browsers which do not support
        // them
        new ProvidePlugin({
            'Promise': 'es6-promise',
            'fetch': 'imports?this=>global!exports?global.fetch!whatwg-fetch'
        // copies image files directly when they are changed
        new CopyWebpackPlugin([{
            from: path.join(srcFolder, 'images'),
            to: path.join('..', 'images')
        // copies the index.html file, and injects a reference to the output JS 
        // file, app.js
        new HtmlWebpackPlugin({
            template: path.join(__dirname, srcFolder, 'index.html'),
            filename:  path.join('..', 'index.html'),
            inject: 'body',
    // output file settings
    // path points to web server content folder where the web server will serve 
    // the files from file name is the name of the files, where [name] is the 
    // name of each entry point 
    output: {
        path: path.join(__dirname, distFolder, 'js'),
        filename: '[name].js',
        publicPath: '/js'
    // use full source maps
    // this specific setting value is required to set breakpoints in they
    // TypeScript source in the web browser for development other source map
    devtool: 'source-map',
    // use the webpack dev server to serve up the web application
    devServer: {
        // files are served from this folder
        contentBase: 'dist',
        // support HTML5 History API for react router
        historyApiFallback: true,
        // listen to port 5000, change this to another port if another server 
        // is already listening on this port
        port: 5000,
        // proxy requests to the JSON server REST service
        proxy: {
            '/widgets': {
                // server to proxy
                target: 'http://0.0.0.0:3010'
Just change from "loaders" to "rules" in "webpack.config.js"
Because loaders is used in Webpack 1, and rules in Webpack2.
You can see there have differences.
Webpack's configuration file has changed over the years (likely with each major release).  The answer to the question:
Why do I get this error 
Invalid configuration object. Webpack has been initialised using a 
configuration object that does not match the API schema
is because the configuration file doesn't match the version of webpack being used. 
The accepted answer doesn't state this and other answers allude to this but don't state it clearly npm install webpack@2.1.0-beta.22, Just change from "loaders" to "rules" in "webpack.config.js", and this.
So I decide to provide my answer to this question.
Uninstalling and re-installing webpack, or using the global version of webpack will not fix this problem.  Using the correct version of webpack for the configuration file being used is what is important.
If this problem was fixed when using a global version it likely means that your global version was "old" and the webpack.config.js file format your using is "old" so they match and viola things now work.  I'm all for things working, but want readers to know why they worked.
Whenever you get a webpack configuration that you hope is going to solve your problem ... ask yourself what version of webpack the configuration is for.  
There are a lot of good resources for learning webpack.  Some are:
Official Webpack website describing the webpack configuration, currently at version 4.x.  While this is a great resource for looking up how webpack should work, it isn't always the best at learning how 2 or 3 options in webpack work together to solve a problem.  But it is the best place to start because it forces you to know what version of webpack you are using. :-)
Webpack (v3?) by Example - takes a bite-sized approach for learning webpack, picking a problem and then showing how to solve it in webpack.  I like this approach. Unfortunately it is not teaching webpack 4 but is still good.
Setting up Webpack4, Babel and React from scratch, revisited - This is specific to React but good if you want to learn many of the things that are required to create a react single page app.
Webpack (v3) — The Confusing Parts - Good and covers a lot of ground.  It is dated Apr 10, 2016 and doesn't cover webpack4 but many of the teaching points are valid or useful to learn.
There are a lot more good resources for learning webpack4 by example, please add comments if you know of others.  Hopefully, future webpack articles will state the versions being used/explained.
                Good part is that the link above, contains tutorial to create your own webpack file for version beyond 4.x + using cli. Which makes it very easy to update your webpack and resolve the issue.
– Saurabh Gupta
                Feb 25 at 11:20
I solved this issue by removing empty string from my resolve array. Check out resolve documentation on webpack's site.
//Doesn't work
module.exports = {
  resolve: {
    extensions: ['', '.js', '.jsx']
//Works!
module.exports = {
  resolve: {
    extensions: ['.js', '.jsx']
                Why doesn't work anymore? In old versions of the webpack i always see the empty string at the first index of extensions array value
– guilima
                Dec 3, 2017 at 13:39
I don't exactly know what causes that, but I solve it this way.

Reinstall whole project but remember that webpack-dev-server must be globally installed. 
I walk through some server errors like webpack cant be found, so I linked Webpack using link command. 
In output Resolving some absolute path issues. 
In devServer object: inline: false
webpack.config.js
module.exports = {
    entry: "./src/js/main.js",
    output: {
        path:__dirname+ '/dist/',
        filename: "bundle.js",
        publicPath: '/'
    devServer: {
        inline: false,
        contentBase: "./dist",
    module: {
        loaders: [
                test: /\.jsx?$/,
                exclude:/(node_modules|bower_components)/,
                loader: 'babel-loader',
                query: {
                    presets: ['es2015', 'react']
package.json
  "name": "react-flux-architecture-es6",
  "version": "1.0.0",
  "description": "egghead",
  "main": "index.js",
  "scripts": {
    "start": "webpack-dev-server"
  "repository": {
    "type": "git",
    "url": "git+https://github.com/cichy/react-flux-architecture-es6.git"
  "keywords": [
    "React",
    "flux"
  "author": "Jarosław Cichoń",
  "license": "ISC",
  "bugs": {
    "url": "https://github.com/cichy/react-flux-architecture-es6/issues"
  "homepage": "https://github.com/cichy/react-flux-architecture-es6#readme",
  "dependencies": {
    "flux": "^3.1.2",
    "react": "^15.4.2",
    "react-dom": "^15.4.2",
    "react-router": "^3.0.2"
  "devDependencies": {
    "babel-core": "^6.22.1",
    "babel-loader": "^6.2.10",
    "babel-preset-es2015": "^6.22.0",
    "babel-preset-react": "^6.22.0"
                simply removing the local install of webpack-dev-server and installing it globally fixed this for me.
– Sam
                Oct 16, 2017 at 10:08
                I think the loaders option  have been replaced with rules see webpack.js.org/concepts/loaders
– Olotin Temitope
                Mar 28, 2018 at 23:48
This error usually happens when you have conflicting version (angular js). So the webpack could not start the application. You can simply fix it by removing the webpack and reinstall it.
npm uninstall webpack --save-dev
npm install webpack --save-dev
The restart your application and everything is fine.
I hope am able to help someone. Cheers
                I had this problem while upgrading a project to a newer version of Angular. Simply reinstalling Webpack worked! Thanks!
– Iván Pérez
                Aug 28, 2019 at 11:12
For the people like myself, who started recently: The loaders keyword is replaced with rules; even though it still represents the concept of loaders. So my webpack.config.js, for a React app, is as follows:
var webpack = require('webpack');
var path = require('path');
var BUILD_DIR = path.resolve(__dirname, 'src/client/public');
var APP_DIR = path.resolve(__dirname, 'src/client/app');
var config = {
  entry: APP_DIR + '/index.jsx',
  output: {
    path: BUILD_DIR,
    filename: 'bundle.js'
  module : {
    rules : [
        test : /\.jsx?/,
        include : APP_DIR,
        loader : 'babel-loader'
module.exports = config;
I guess your webpack version is 2.2.1. I think you should be using this Migration Guide -->  https://webpack.js.org/guides/migrating/
Also, You can use this example of TypeSCript + Webpack 2.
I had the same issue and I solved it by installing latest npm version:
npm install -g npm@latest
and then change the webpack.config.js file to solve 
- configuration.resolve.extensions[0] should not be empty.
now resolve extension should look like:
resolve: {
    extensions: [ '.js', '.jsx']
then run npm start.
                This worked for me. In my webpack.config.js file, I had an entry such as extentions:[ '', '.js', '.jsx']. I removed the empty item '' and it worked.  configuration.resolve.extensions[0] refers to the first item under resolve: { extensions:['', '.js', '.jsx']} in webpack.config.js file.
– Ajitesh
                Sep 12, 2017 at 7:33
I got the same error message when introducing webpack to a project I created with npm init.
Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
   - configuration.output.path: The provided value "dist/assets" is not an absolute path!
I started over using yarn which fixed the problem for me:
brew update
brew install yarn
brew upgrade yarn
yarn init
yarn add webpack webpack-dev-server path
touch webpack.config.js
yarn add babel-loader babel-core babel-preset-es2015 babel-preset-react --dev
yarn add html-webpack-plugin
yarn start
I found the following link helpful:
Setup a React Environment Using webpack and Babel
                I tried this, all working fine except there are some warnings but when I do the last commend "yarn start", it gives me an error "Command start not found", do u know how to fix this? Thx!
– Tony Chen
                Jul 8, 2017 at 3:54
I had the same issue and I resolved this by making some changes in my web.config.js file. FYI I am using the latest version of webpack and webpack-cli. This trick just saved my day. I have attached the example of mine web.config.js file before and after version.
Before:
module.exports = {
    resolve: {
        extensions: ['.js', '.jsx']
    entry: './index.js',
    output: {
         filename: 'bundle.js'
    module: {
        loaders : [
           { test: /\.js?/, loader: 'babel-loader', exclude: /node_modules/ }
After: I Just replaced loaders to rules in module object as you can see in my code snippet.
module.exports = {
    resolve: {
        extensions: ['.js', '.jsx']
    entry: './index.js',
    output: {
        filename: 'bundle.js'
    module: {
        rules : [
            { test: /\.js?/, loader: 'babel-loader', exclude: /node_modules/ }
Hopefully, This will help someone to get rid out of this issue.
A somewhat unlikely situation.
I have removed the yarn.lock file, which referenced an older version of webpack.
So check to see the differences in your yarn.lock file as a possiblity.
  Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
   - configuration.entry should be one of these:
     function | object { : non-empty string | [non-empty string] } | non-empty string | [non-empty string]
     -> The entry point(s) of the compilation.
     Details:
      * configuration.entry should be an instance of function
        -> A Function returning an entry object, an entry string, an entry array or a promise to these things.
      * configuration.entry['styles'] should be a string.
        -> The string is resolved to a module which is loaded upon startup.
      * configuration.entry['styles'] should not contain the item 'C:\MojiFajlovi\Faks\11Master\1Semestar\UDD-UpravljanjeDigitalnimDokumentima\Projekat\
  nc-front\node_modules\bootstrap\dist\css\bootstrap.min.css' twice.
As the bold-ed error message line said, I just opened angular.json file and found the styles to look like this:
"styles": [
      "./node_modules/bootstrap/dist/css/bootstrap.min.css",
      "src/styles.css",
      "node_modules/bootstrap/dist/css/bootstrap.min.css" <-- **marked line**
... so I just removed the marked line...
and it all went well. :)
If you are coming from the single SPA world, and you encounter this error. I realized the issue is caused by the scripts to serve the application.
An example is this:
"scripts": {
    "start": "ng serve",
    "serve:single-spa:play": "ng s --project play --disable-host-check --port 4202 --deploy-url http://localhost:4202/ --live-reload false"
To make this work, change the start script to the one below:
"scripts": {
    "start": "npm run serve:single-spa:play",
    "serve:single-spa:play": "ng s --project play --disable-host-check --port 4202 --deploy-url http://localhost:4202/ --live-reload false"
If you encounter this error after migrating angular version from 11 to 12 and using single spa,
then you can configure "package.json" for the below packages
"single-spa": "^5.9.3"
"single-spa-angular": "^5.0.2"
"@angular-builders/custom-webpack": "^12.1.3"
"webpack": "^5.70.0"
after npm install
For Expo projects
If you are using Expo SDK version 45 you'll need to use Expo CLI 6.1.0 at most. Higher versions of the CLI will throw this error:
ValidationError: Invalid configuration object. Webpack has been initialized using a configuration object that does not match the API schema.
 - configuration.node should be one of these:
   false | object { __dirname?, __filename?, global? }
   -> Include polyfills or mocks for various node stuff.
   Details:
    * configuration.node has an unknown property 'module'. These properties are valid:
      object { __dirname?, __filename?, global? }
      -> Options object for node compatibility features.
    * configuration.node has an unknown property 'dgram'. These properties are valid:
      object { __dirname?, __filename?, global? }
(continues)
To fix the problem, install the version 6.1.0 of the expo-cli with npm install -g expo-cli@6.1.0.
Also take a look at https://github.com/expo/expo-cli/issues/4639 where there are other solutions.
Aside: Expo SDK 46 no longer requires a global CLI package. See The New Expo CLI and the Expo SDK 46 announcement.
                wow! that's it! also had an outdated project in a node version, where i somewhen upgraded the expo cli. thanks, the downgrade helped!
– Donni
                Mar 28 at 8:22
I ran into this problem while trying to use WebPack5 with Cypress and Cucumber (based off of this example https://github.com/TheBrainFamily/cypress-cucumber-webpack-typescript-example). Changing plugin\index.js to this worked for me!
const browserify = require('@cypress/browserify-preprocessor');
const cucumber = require('cypress-cucumber-preprocessor').default;
module.exports = (on, config) => {
  const options = {
    ...browserify.defaultOptions,
    typescript: require.resolve('typescript'),
  on('file:preprocessor', cucumber(options));
  on('task', {
    log(message) {
      console.log(message)
      return null