Conflict: Multiple assets emit to the same filename

I'm a webpack rookie who wants to learn all about it. I came across a conflict when running my webpack telling me:

> ERROR in chunk html [entry] app.js Conflict: Multiple assets emit to > the same filename app.js

What should I do to avoid the conflict?

This is my webpack.config.js:

module.exports = {
  context: __dirname + "/app",

  entry: {
    'javascript': "./js/app.js",
    'html': "./index.html",
  },
  output: {
    path: __dirname + "/dist",
    filename: "app.js",
  },
  resolve: {
    extensions: ['.js', '.jsx', '.json']
  },
  module: {
    loaders: [
      {
        test: /\.jsx?$/,
        exclude: /node_modules/,
        loaders: ["babel-loader"]
      },
      {
        test: /\.html$/,
        loader: "file-loader?name=[name].[ext]",
      }
    ]
  }
};

i'm not quite familiar with your approach so I'll show you a common way to help you out.

First of all, on your output, you are specifying the filename to app.js which makes sense for me that the output will still be app.js. If you want to make it dynamic, then just use "filename": "[name].js".

The [name] part will make the filename dynamic for you. That's the purpose of your entry as an object. Each key will be used as a name in replacement of the [name].js.

And second, you can use the html-webpack-plugin. You don't need to include it as a test.

I had the same problem, I found it was setting a static output file name that was causing my problem, in the output object try the following object.

output:{
        filename: '[name].js',
        path: __dirname + '/build',
        chunkFilename: '[id].[chunkhash].js'
    },

This makes it so that the filenames are different and it doesn't clash.

EDIT: One thing i've recently found is that you should use a hash instead of chunkhash if using HMR reloading. I haven't dug into the root of the problem but I just know that using chunkhash was breaking my webpack config

output: {
  path: path.resolve(__dirname, 'dist'),
  filename: '[name].[hash:8].js',
  sourceMapFilename: '[name].[hash:8].map',
  chunkFilename: '[id].[hash:8].js'
};

Should work fine with HMR then :)

EDIT July 2018:

A little more information on this.

Hash This is a hash generated every time that webpack compiles, in dev mode this is good for cache busting during development but shouldn't be used for long term caching of your files. This will overwrite the Hash on every build of your project.

Chunkhash If you use this in conjunction with a runtime chunk then you can use it for long term caching, the runtime chunk will see what's changed in your source code and update the corresponding chunks hash's. It won't update others allowing for your files to be cached.

I had exactly the same problem. The problem seems to occur with the file-loader. The error went away when I removed the html test and included html-webpack-plugin instead to generate an index.html file. This is my webpack.config.js file:

var path = require('path');

var HtmlWebpackPlugin = require('html-webpack-plugin');
var HTMLWebpackPluginConfig = new HtmlWebpackPlugin({
  template: __dirname + '/app/index.html',
  filename: 'index.html',
  inject: 'body'
})

module.exports = { 
  entry: {
    javascript: './app/index.js',
  },  

  output: {
    filename: 'bundle.js',
    path: __dirname + '/dist'
  },  

  module: {
    rules: [
      {   
        test: /\.jsx?$/,
        exclude: [
          path.resolve(__dirname, '/node_modules/')
        ],  
        loader: 'babel-loader'
      },  
    ]   
  },  

  resolve: {
    extensions: ['.js', '.jsx', '.json']
  },  

  plugins: [HTMLWebpackPluginConfig]
}

The html-webpack-plugin generates an index.html file and automatically injects the bundled js file into it.

I had the same issue after upgrading to Webpack 5. My problem was caused by the copy-webpack-plugin.

Below is the original pattern ignoring a specified file, it works with Webpack 4, but throws an error with Webpack 5.

> ERROR in Conflict: Multiple assets emit different content to the same > filename default.hbs

  plugins: [
   new CopyPlugin({
      patterns: [
        {
          from: "./src/academy/templates",
          globOptions: {
            ignore: ["default.hbs"]
          }
        },
      ]
    }),
   ],

To fix the error:

  plugins: [
   new CopyPlugin({
      patterns: [
        {
          from: "./src/academy/templates",
          globOptions: {
            ignore: ["**/default.hbs"]
          }
        },
      ]
    }),
   ],

By not ignoring the specified file, the default.hbs (a.k.a index.html) was copied twice into the build (a.k.a /disk) directory effectively resulting in Webpack trying to insert multiple assets into the "same" (duplicated) filename.

I had the same problem, and I found these in the documents.

> If your configuration creates more than a single “chunk” (as with multiple entry points or when using plugins like CommonsChunkPlugin), you should use substitutions to ensure that each file has a unique name.

>

• [name] is replaced by the name of the chunk.

• [hash] is replaced by the hash of the compilation.

• [chunkhash] is replaced by the hash of the chunk.

  output: { path:__dirname+'/dist/js',

   //replace filename:'app.js' 
   filename:'[name].js'
  

  }

In my case the source map plugin was conflicting with the extract mini plugin. Could not find a solution to this anywhere. source maps for css and javascript were writing to the same file. Here is how I finally solved it in my project:

new webpack.SourceMapDevToolPlugin({
    filename: '[name].[ext].map'
}),

I encountered this error in my local dev environment. For me, the solution to this error was to force the files to rebuild. To do this, I made a minor change to one of my CSS files.

I reloaded my browser and the error went away.

I changed index.html file from /public directory to /src to fix this issue. (Webpack 5.1.3)

I had the same problem after updating all the dependencies to latest (e.g. webpack 4 -> 5) for a Chrome extension I made about 2 years ago, and managed to solve it.

There were two files in the complaint (popup.html and options.html). Here is my original webpack.config.js file:

const path = require('path');
const CopyPlugin = require('copy-webpack-plugin');
const HtmlWebpackPlugin = require("html-webpack-plugin");
const { CleanWebpackPlugin } = require("clean-webpack-plugin");

module.exports = {
    target: 'web',
    output: {
        path: path.resolve(__dirname, 'dist'),
        filename: '[name].js',
    },
    entry: {
        popup: './src/scripts/popup.tsx',
        options: './src/scripts/options.tsx',
    },
    context: path.join(__dirname),
    module: {
        rules: [
            {
                test: /\.tsx?$/,
                loader: 'ts-loader',
            },
            {
                test: /\.css$/,
                use: [
                    'style-loader',
                    'css-loader',
                ],
            },
            {
                test: /\.scss$/,
                use: [
                    'style-loader',
                    'css-loader',
                    'sass-loader',
                ],
            },
        ],
    },

    resolve: {
        extensions: ['.tsx', '.ts', '.js', '.json', '.css'],
    },
    plugins: [
        new CleanWebpackPlugin(),
        new CopyPlugin([
            { from: 'src/popup.html', to: 'popup.html' },
            { from: 'src/options.html', to: 'options.html' },
            { from: 'src/manifest.json', to: 'manifest.json' },
            { from: 'src/icons', to: 'icons' },
        ]),
        new HtmlWebpackPlugin({
            template: path.join("src", "popup.html"),
            filename: "popup.html",
            chunks: ["popup"]
        }),
        new HtmlWebpackPlugin({
            template: path.join("src", "options.html"),
            filename: "options.html",
            chunks: ["options"]
        }),
    ]
};

I solved it by removing:

            { from: 'src/popup.html', to: 'popup.html' },
            { from: 'src/options.html', to: 'options.html' },

under new CopyPlugin... part.

So seems like right now there is no need to explicitly copy popup.html and options.html to output folder when HtmlWebpackPlugin is already emitting them.

Similar solution to the above with file-loader, however, I think this solution is the more elegant. Before, I was only specifying the [name], adding the [path][name] resolved my conflict as below:

module: {
rules: [
  {
    test: /\.(mp4|m4s)$/,
    use: [
      {
        loader: 'file-loader',
        options: {
          name: '[path][name].[ext]',
        },
      },
    ],
  },
],

The same error in a Vue.js project when doing e2e with Karma. The page was served using a static template index.html with /dist/build.js. And got this error running Karma.

The command to issue Karma using package.json was:

"test": "cross-env BABEL_ENV=test CHROME_BIN=$(which chromium-browser) karma start --single-run"

The output configuration in webpack.config.js was:

 module.exports = {
  output: {
   path: path.resolve(__dirname, './dist'),
   publicPath: '/dist/',
   filename: 'build.js'
  },
  ...
 }

My solution: inspired by the Evan Burbidge's answer I appended the following at the end of webpack.config.js:

if (process.env.BABEL_ENV === 'test') {
  module.exports.output.filename = '[name].[hash:8].js'
}

And then it eventually worked for both page serving and e2e.

I had a similar problem while upgrading webpack 3 to webpack 4. After upgrading the modules I came across this error.

>WARNING in Conflict: Multiple assets emit different content to the same filename alert-icon.svg > > WARNING in Conflict: Multiple assets emit different content to the same filename comment.svg

The problem was caused by fileloader for svg. Solved the error by adding a hash name: '[name].[hash:8].[ext]' making it unique every time webpack compiles.

Provinding the code below:

module: {
rules: [
  {
  test: /\.svg$/,
  loader: 'file-loader',
  query: {
    name: '[name].[hash:8].[ext]'
  }  
]   

}