tntruong96/webpack-interview-questions

Webpack questions/answers you can use to prepare for interviews or test your knowledge.

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