Unlocking the Secret to Smaller Bundle Sizes
The Problem with Modern JavaScript Applications
Most modern JavaScript-heavy applications are guilty of shipping far too much code to the browser. The result? Bloated bundle sizes that slow down page loads and frustrate users. But why does this happen? Often, it’s because libraries like Formik include unnecessary modules, doubling their size and dragging down performance.
The Solution: Eliminating Dead Code
To combat this issue, we need a way to eliminate dead code and only import the modules that are actually used. This requires static analysis on the codebase, which can be challenging. However, by switching to ESM (Ecmascript) module syntax, we can facilitate static analysis and reduce bundle size.
The Limitations of CommonJS
CommonJS modules, on the other hand, are harder to optimize due to dynamic imports and exports. This means that static analyzers will often grab everything, resulting in larger bundle sizes. By contrast, ESM modules provide a clear and concise way of importing and exporting modules, making it easier to identify and eliminate dead code.
Rollup: The Market Leader in Dead Code Elimination
Rollup is a bundler that excels at eliminating dead code. Unlike Webpack, which wraps each module in a function, Rollup uses scope hoisting to put all code at the same level. This approach results in smaller bundles with less overhead. The trade-off is that Rollup relies on ESM module semantics, making it essential to convert CommonJS packages to 100% ESM packages.
Package.json Module Resolution
When it comes to package.json module resolution, bundlers like Rollup and Webpack have mechanisms to specify which field is the entry point. By setting the type field to module and supplying a module field, we can ensure that our packages are ESM compliant.
Gotchas and Workarounds
However, there are some gotchas to watch out for. For example, files with an .mjs extension are treated differently by Webpack and Rollup. To avoid issues, it’s best to output files with a .esm.js extension. Additionally, dependencies like React and react-router may require special handling to ensure ESM compliance.
Configuring Rollup for Success
To get the most out of Rollup, we need to configure it correctly. This involves using plugins like @rollup/plugin-node-resolve and rollup-plugin-typescript2 to ensure that our code is transpiled to ESNext. By following these steps, we can create ESM compliant packages with smaller bundle sizes.
The Future of JavaScript Development
As the world slowly moves towards ESM modules, it’s clear that the benefits of smaller bundle sizes and improved performance are too great to ignore. Whether you’re using Rollup or Webpack, it’s time to make the switch to ESM modules and start building faster, more efficient applications.