20 Compiling in Next.js

Compiling is a fundamental process in Next.js application development that transforms the source code into a form that can be executed in the browser. Next.js uses Webpack and Babel behind the scenes to enable efficient compilation and bundling of resources.

20.1 Webpack in Next.js

Webpack is a module bundler used in Next.js to bundle JavaScript and other files. It allows merging modules and assets such as JavaScript, CSS and images into a few compiled files to optimize loading times.

20.1.1 Customizing the webpack configuration

In Next.js you can customize the webpack configuration via the next.config.js file. This allows you to define custom webpack loaders, plugins and other settings.

20.1.1.1 Example:

module.exports = {
  webpack: (config, { buildId, dev, isServer, defaultLoaders, webpack }) => {
    // Adjustments here
    return config;
  },
};

20.2 Babel in Next.js

Babel is a JavaScript compiler that makes it possible to translate modern ES6+ JavaScript into a backwards-compatible version that works in older browsers. Next.js configures Babel by default for optimal performance and compatibility.

20.2.1 Customizing the Babel configuration

You can customize the Babel configuration in Next.js by adding a .babelrc or babel.config.js file in your project.

20.2.1.1 Example:

module.exports = {
  presets: ['next/babel'],
  plugins: [],
};

20.3 Optimizations during compilation

Next.js performs several optimizations during the compilation process, including:

1. Code splitting: Next.js automatically splits the code into different bundles so that only the code needed for the current page is loaded.

2. Tree Shaking: Removes unused code from the bundles to reduce the size.

3. Minimization: Minimizes JavaScript and CSS to reduce file sizes.

4. Automatic polyfills: Adds polyfills based on the browsers you want to support.