20 Years of JavaScript Modules: Chaos, Fragmentation, and a Path Forward

1. Introduction: Have We Really Solved "Modularity"?

You might think JavaScript's module system is fully standardized—import/export is the end of the story.

But in reality, build errors, dependency conflicts, and load failures are still common.

From <script> to require() to import/export, we’ve been paying the price for historical architecture decisions.

Modules were meant to simplify complexity—but in JavaScript, they’ve often become landmines.

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2. A Brief History of Chaos: Two Decades, Many Heads

1. The Era Without Modules (Early 2000s)

JavaScript was never designed with modularity in mind. Everything lived in the global scope.
Scripts loaded in order, and naming collisions were a constant fear.

2. Community Workarounds

As official support lagged, the community invented pseudo-solutions like IIFE, namespace objects, and the revealing module pattern.
These were clever but incompatible, hard to scale, and lacked ecosystem-wide support.

3. Node.js Introduces CommonJS

Node brought in require() and module.exports, formalizing modularity—at least on the server side.
Browsers didn’t support it, so tools like Browserify and Webpack emerged to bridge the gap.

4. The Arrival of ES Modules (ESM)

ES6 introduced import/export to great excitement.
But it was too late—CommonJS had already taken deep root, and build tools had grown monstrous.
Now, module format isn’t just syntax—it’s a negotiation between tools.

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3. The Real Cost of Modularity

Errors like "Cannot use import outside a module" or "SyntaxError: Unexpected token 'export'" aren’t just syntax issues.
They reflect deep fractures left by 20 years of inconsistent module support.

Tree shaking often fails, bundles get bloated, and performance suffers.
Publishing a package means generating CJS, ESM, UMD—each with its own quirks.
What should simplify collaboration has become a major source of complexity.

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4. CommonJS vs. ESM: Differences and Compatibility Pitfalls

CommonJS (CJS) and ECMAScript Modules (ESM) have coexisted in Node.js—creating lasting technical debt.

Let’s break down key differences:

• Syntax:

  • CJS uses require() and module.exports.
  • ESM uses import and export, enabling static analysis and tree shaking.

• Load Behavior:

  • CJS loads modules synchronously.
  • ESM loads asynchronously and requires top-level import.

• Tree Shaking:

  • ESM supports dead code elimination.
  • CJS doesn’t, due to dynamic loading.

• Path Handling:

  • CJS gives us __dirname, __filename.
  • ESM requires using import.meta.url with extra steps:

  import { fileURLToPath } from 'node:url';
  import { dirname } from 'node:path';
  
  const __filename = fileURLToPath(import.meta.url);
  const __dirname = dirname(__filename);
  

• Interoperability:

  • Use createRequire() in ESM to load CJS modules.

  import { createRequire } from 'node:module';
  const require = createRequire(import.meta.url);
  const lodash = require('lodash');
  

  • Use await import() in CJS to load ESM modules. Node 23+ even allows require() for ESM modules without top-level await:

  const esm = require('./esm-file.mjs');
  console.log(esm);
  

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5. Migration Strategies That Actually Work

For new projects, go with ESM—it’s the cleaner, modern starting point.

But legacy projects face structural differences in loading, resolution, caching, and interop.

Here’s how you can migrate safely:

• Gradual migration:
  Keep CJS as base, convert key modules to ESM, and use dynamic import().

• Layered testing:
  Add test boundaries around each module change.

• Node.js 23+ features:
  These help bridge CJS-to-ESM with fewer toolchain hacks.

• Use ServBay:
  A modern local development platform for Node.js. It supports .mjs, "type": "module", and hybrid ESM/CJS testing out of the box—making CI/CD less painful.

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6. A Message to JavaScript Developers

JavaScript’s module system was never designed—it was patched together.

First no modules at all, then CommonJS, then ESM… all layered with tooling and polyfills.

The result? Modularity became a historical burden, not a solved problem.

It’s not your fault when import fails. You’re navigating a fractured ecosystem.

As Maxime said in Modules in JavaScript: A 20-Year Mistake:

“We didn’t build a module system. We built a compatibility layer on top of 20 years of mess.”

Even so, migrating is still worth it.
It boosts build efficiency, supports modern APIs, and future-proofs your stack.

You don’t have to rewrite overnight—just start.
Adopt best practices gradually.
Fix legacy interfaces step by step.

And remember:
Modules are here to organize your code—not to make your life harder.
Use tools and knowledge to move forward, not to repeat the past.