If you've been dabbling in modern JavaScript development, you've likely come across Babel and its powerful preset ecosystem. One common pain point that developers often face is understanding the `useBuiltIns` option in Babel's `@babel/preset-env` plugin, especially when it comes to integrating with Browserslist configuration. It can be confusing at first, but fear not - we're here to break it down for you!
Let's start by clarifying what the `useBuiltIns` option actually does. Essentially, `useBuiltIns` allows you to automatically import the necessary polyfills based on the browsers you're targeting, instead of manually including them in your code. This helps keep your bundle size optimized by only including polyfills for features that are actually needed based on your specified browser support.
When using `@babel/preset-env` with `useBuiltIns`, you need to leverage a Browserslist configuration file to define the target environments for your project. Browserslist is a popular tool that lets you specify the range of browser versions you want to support, and it's used by various frontend tools including Autoprefixer and Babel.
To start, create a `.browserslistrc` file in the root of your project or add a `browserslist` key in your `package.json`. In this file, list the browsers you want to support based on your project requirements. For example, you could have entries like `last 2 versions` or `> 1%` to cover a broad range of modern browsers.
Once you have your Browserslist configuration set up, you can now configure `@babel/preset-env` in your Babel configuration file (e.g., `.babelrc` or `babel.config.js`). Include the `useBuiltIns` option with either `'entry'` or `'usage'` as its value.
- Use `'entry'` if you want Babel to include all necessary polyfills upfront in your bundle, regardless of whether the features are used in your code or not.
- Use `'usage'` if you prefer Babel to only import polyfills for features that are actually used in your code, resulting in a more optimized bundle size.
Here's an example of how you can set up `@babel/preset-env` with `useBuiltIns` in your Babel configuration:
{
"presets": [
["@babel/preset-env", {
"useBuiltIns": "usage",
"corejs": 3
}]
]
}In this example, we specified `'usage'` for `useBuiltIns` and included `core-js@3` as the polyfill source. Make sure to install `core-js` as a dependency in your project using `npm install core-js`.
With this setup, Babel will intelligently import only the polyfills needed based on your actual code usage and your specified browser support defined in the Browserslist configuration.
By leveraging the power of `useBuiltIns` in Babel's `@babel/preset-env` plugin alongside Browserslist integration, you can streamline your JavaScript development workflow and ensure that your applications are compatible with the target browsers you aim to support. So, dive in, experiment with different configurations, and optimize your code for a smoother cross-browser experience!