Webpack interview questions

View version with answers

Big thanks to TheLarkInn, raybooysen and johannesMatevosyan for contribution.

Table of Contents

• Concepts
• Config file
• Loaders
• Plugins
• Development
• Optimization
• Migration
• Advanced questions
• Internal API Questions (very advanced)

Concepts

• What is webpack?
• What is the main difference between webpack and other build tools like gulp or grunt?
• What is a bundle in webpack?
• In which environment does webpack work?
• What is an entry point?
• What is a dependency graph and how does webpack build it?
• Which modules design patterns webpack supports out of the box?

Config file

• What is the format of webpack's config file?
• Is it possible to have multiple entry points in a single webpack configuration file?
• Is it possible to define multiple configurations for different environments?
• How can we generate webpack config file automatically?

Loaders

• What is a loader in webpack?
• Where should loaders be defined?
• What is the difference between a rule and a loader?
• Explain this code

  {
    test: /\.scss$/,
    loaders: ['style-loader', 'css-loader?sourceMap', 'sass-loader?sourceMap', 'postcss-loader'],
    exclude: /node_modules/
  }
  

• Do loaders work in a synchronous or an asynchronous way?
• Is it possible to use multiple loaders in the rules single object?
• Name loaders that you think are very important and helpful.

Plugins

• Describe a plugin in webpack.
• What is the difference between a loader and a plugin?
• What is the advantage of CompressionPlugin?
• How can you move some data (e.g css code) from a bundle to a separate file in webpack?
• Name some plugins you think are important and helpful.
• Is it possible to write your own plugin?

Development

• What are some advantages of using webpack-dev-server over simple http server or nginx?
• On which platform is webpack-dev-server developed?
• What is Hot-Modules-Replacement?
• Does it make sense to use Hot-Modules-Replacement in production environment?
• How to enable source maps in webpack bundles?
• How to automatically build and update bundles in the browser after a change in source code?
• What is parallel-webpack and how does it affect webpack's build process?

Optimization

• Briefly describe long-term caching and how to achieve it using webpack?

• What is difference between

     ...
     output: {
      filename: "[name].[hash].js"
     }
     ...
  

  and

     ...
      output: {
       filename: "[name].[chunkhash].js"
      }
      ...
  

• Describe the CommonsChunkPlugin.

• Explain this code

   new webpack.optimize.CommonsChunkPlugin({
     name: 'common',
     filename: 'common.js',
     chunks: ['home', 'dashboard']
   })

• Which built-in plugin should be used for code minification?
• Explain this code

   new webpack.ContextReplacementPlugin(
     /moment[\/\\]locale/,
     /(en-gb|en-us)\.js/
   )

• How to remove unused selectors from css using webpack?
• How to achieve lazy loading in webpack?
• Why is OccurenceOrderPlugin part of webpack optimization? What it has to do with module ids and topological sorting?
• What analysis tools do you use for webpack bundle's inspection?

Migration

• Describe the LoaderOptionsPlugin.
• Do you need to include OccurenceOrderPlugin in the plugins section when use webpack 2/3?
• Which version(s) of webpack support es6 modules out the box?
• Which version(s) of webpack support json-loader out the box?
• Which version(s) of webpack support code splitting?

Advanced questions

• Describe the webpack runtime and manifest.
• Is it possible to use other languages (except javascript) for the webpack config file?
• Is it possible to have different configuration files for different environments?
• Describe the tree shaking mechanism.
• What is the difference between tree shaking and dead code elimination.
• Describe scope hoisting in webpack 3.
• What is Tapable and how does it relate to webpack plugins?

Internal API Questions (very advanced)

• What is the difference between Compiler and Watching classes?
• Describe the purpose of Compiler
• Describe the purpose of Compililation
• Describe DependenciesBlock class. Why is it so important?
• Describe the relationship between the Parser, Dependency, Dependency Factory, and Dependency Templates