Explain the concept of tree shaking in module bundling

TL;DR

Tree shaking is a technique used in module bundling to eliminate dead code, which is code that is never used or executed. This helps to reduce the final bundle size and improve application performance. It works by analyzing the dependency graph of the code and removing any unused exports. Tools like Webpack and Rollup support tree shaking when using ES6 module syntax (import and export).

The concept of tree shaking in module bundling

Tree shaking is a term commonly used in the context of JavaScript module bundlers like Webpack and Rollup. It refers to the process of eliminating dead code from the final bundle, which helps in reducing the bundle size and improving the performance of the application.

How tree shaking works

Tree shaking works by analyzing the dependency graph of the code. It looks at the import and export statements to determine which parts of the code are actually used and which are not. The unused code, also known as dead code, is then removed from the final bundle.

Example

Consider the following example:

// utils.js
export function add(a, b) {
  return a + b;
}

export function subtract(a, b) {
  return a - b;
}

// main.js
import { add } from './utils';

console.log(add(2, 3));

In this example, the subtract function is never used in main.js. A tree-shaking-enabled bundler will recognize this and exclude the subtract function from the final bundle.

Requirements for tree shaking

1. ES6 module syntax: Tree shaking relies on the static structure of ES6 module syntax (import and export). CommonJS modules (require and module.exports) are not statically analyzable and thus not suitable for tree shaking.
2. Bundler support: The bundler you are using must support tree shaking. Both Webpack and Rollup have built-in support for tree shaking.

Tools that support tree shaking

• Webpack: Webpack supports tree shaking out of the box when using ES6 modules. You can enable it by setting the mode to production in your Webpack configuration.
• Rollup: Rollup is designed with tree shaking in mind and provides excellent support for it.

Benefits of tree shaking

• Reduced bundle size: By removing unused code, the final bundle size is reduced, leading to faster load times.
• Improved performance: Smaller bundles mean less code to parse and execute, which can improve the performance of your application.

Further reading

• Webpack Tree Shaking
• Rollup Tree Shaking
• MDN Web Docs: Import
• MDN Web Docs: Export