Future-Proof ECMAScript with Compilers and Polyfills

In my previous article, I shared a list of all major features introduced across different versions of ECMAScript. But a crucial question arises:

Can we use all these features without facing any compatibility issues, especially in browser environments?

We’ll explore how you can manage ECMAScript compatibility across different environments, ensuring you can utilize the latest language features while maintaining broad compatibility.

Why Compatibility is Crucial for Modern Development

JavaScript runtimes?—?such as browsers and server-side environments like Node.js?—?vary in their support for ECMAScript features. While modern browsers and runtimes are usually quick to adopt the latest versions of ECMAScript, older browser environments often lag behind, creating potential compatibility issues for developers.

Note: For server environments like Node.js, compilers and polyfills are generally not necessary, unless you are using TypeScript. We’ll discuss this in more detail in future articles.

For example, imagine implementing a modern feature like Optional Chaining, only to discover that it crashes in older browsers. This is a common challenge developers face when using new ECMAScript features in an ecosystem that includes older runtimes.

This is where compilers and polyfills come into play. These tools allow you to write modern, clean code using the latest ECMAScript features while ensuring that your code runs smoothly across all target environments.

What is a Compiler?

A compiler is a tool that translates your modern ECMAScript code into a version of JavaScript that is compatible with older runtimes. In simple terms, it rewrites your modern code into older syntax so that it works on unsupported runtimes.

Compilers are typically used before deployment during the build phase, either manually or via build systems like Webpack or Parcel.

Let’s take a look at some of the most popular JavaScript compilers and the toolchains that use them:

• Babel is one of the most popular JavaScript compilers, widely used for transpiling modern ECMAScript (ES6+) into ES5 to ensure compatibility across browsers and environments. Used by: create-react-app, Gatsby, and Storybook.
• TypeScript is a statically typed superset of JavaScript that compiles down to plain JavaScript. Used by: Angular CLI, NestJS, create-react-app (with TypeScript).
• SWC (Speedy Web Compiler) is a Rust-based JavaScript and TypeScript compiler focused on optimizing performance and compilation speed. Used by: create-next-app (Next.js), Docusaurus, and Remix.
• esbuild is a high-speed JavaScript bundler and compiler. It transforms and bundles JavaScript, including TypeScript and JSX, at lightning speed. Used by: Vite, Snowpack, and Astro.

While compilers focus on converting modern syntax into older formats, polyfills go a step further by simulating newer ECMAScript functionalities in environments that don’t support them.

What is a Polyfill?

A polyfill is a piece of code that “fills in” missing ECMAScript features in environments that don’t natively support them. While compilers handle syntax compatibility, polyfills provide functionality that may not exist in older environments, allowing developers to write modern code without worrying about missing features.

Polyfills can either be written manually or integrated through trusted libraries and services, such as:

Popular Polyfills

• core-js: The most popular polyfill for the JavaScript standard library, supporting the latest ECMAScript features. core-js integrates during the build process, typically via tools like Webpack or Babel.
• Polyfill.io: A service that detects which browser is requesting resources and serves the appropriate polyfills based on the browser's capabilities. As a hosted service (hosted by cdnjs.com), it is constantly updated, meaning you don’t need to manually keep up with the latest polyfills.

For modern projects focused on performance and reducing bundle sizes for modern browsers, Polyfill.io is the better choice since it dynamically serves polyfills based on the browser.

For controlled environments where you need to ensure full compatibility across specific target browsers or when optimizing for performance at runtime (avoiding network requests), core-js is the better fit.

SECURITY ALERT: Use Polyfill.io service either from cdnjs or fastly

Choosing Between Compilers and Polyfills

Now that we understand what compilers and polyfills do, how do you decide which one to use?

When to Use a Compiler:

• Syntax Compatibility: If your project uses modern ECMAScript syntax (like classes, arrow functions, or modules), compilers like Babel or SWC will transpile this into versions compatible with older environments.
• Performance: Compilers are excellent for optimizing your codebase and ensuring that your code is modern but compatible with older browsers.

When to Use a Polyfill:

• Missing Functions: Polyfills are necessary when runtimes lack support for specific ECMAScript features. For example, if your code relies on Promises, fetch, or Array.prototype.includes(), polyfills ensure older browsers support these features.

Using Both Together:

In many cases, both compilers and polyfills can be used together. Compilers handle syntax transformations, while polyfills address missing functionality in older environments. By using both tools, you can ensure your code is robust and compatible across a wide range of environments.

Note: Overusing Static polyfills can increase your bundle size and negatively impact performance. To avoid this, use tools like core-js to include only the necessary polyfills based on your target environments.

Conclusion: Bridging the ECMAScript Compatibility Gap

Compilers and polyfills are essential tools for managing ECMAScript compatibility across different runtimes. They allow developers to leverage modern ECMAScript features while ensuring their code remains functional across older environments. By using compilers like Babel or SWC and polyfills for missing features, you can build robust, scalable applications that work seamlessly across various browsers and runtimes.

Next Steps:

In future articles, we’ll dive deeper into setting up compilers for your projects and explore how to effectively integrate polyfills into your build pipeline. Stay tuned for code examples and best practices to enhance your workflow!