Your JavaScript module system architecture gets less thought than it deserves. Most of us treat imports and exports like a grocery list, adding lines until the file works. Every time you link two files you are making an architectural decision that sets your app’s performance, how testable it is, and how far the damage spreads when something breaks.
I have watched enterprise WordPress builds come apart, and it was almost never the database. It was a front end that had turned into a web of circular dependencies. If you do not design the boundaries, your dependencies will design them for you, and the first fork in that road is ECMAScript Modules (ESM) against CommonJS (CJS).
ESM vs. CommonJS: flexibility against analyzability
Moving from CommonJS (require) to ESM (import) changed more than the syntax. It changed what a build tool can work out ahead of time. In CommonJS, require() is a function, so you can call it inside an if statement or a loop. That is flexible for you and miserable for the bundler.
// CommonJS — Dynamic and hard to analyze
if (isProduction) {
const logger = require('./prodLogger');
}
// ESM — Static and predictable
import { logger } from './logger'; // Must be at the top levelESM insists that imports are static string literals at the top of the file, which is what lets bundlers do tree-shaking. They can see which functions you actually use before any of the code runs. That is the part of this JavaScript module system architecture decision that shows up in your final bundle size. With CJS, the bundler often ships the whole library, because it has no way to know what you will ask for at runtime.
Designing a JavaScript module system architecture that lasts
On a large project I lean on Clean Architecture. Robert C. Martin’s Dependency Rule says dependencies point inward, toward your business logic, and never the other way. Your core entities should have no idea that a framework like React or a library like Axios exists.
Look at the module graph rather than guessing at it. Madge and Dependency Cruiser will both draw it for you. A healthy graph looks like a pyramid. An unhealthy one looks like a bowl of spaghetti. If utils.js imports api.js and api.js imports utils.js back, you have a circular dependency, and it will take out your dev server or produce race conditions sooner or later.
The same rules turn up elsewhere in the stack. My guide to Clean CSS Architecture covers how state-driven design keeps styles from leaking.
The barrel file performance trap
Everyone has used barrel files, the index.js that re-exports everything in a folder. They make imports look clean, and they are frequently where the build time goes: pull one component out of a barrel and the engine may have to resolve every file that barrel exports.
Atlassian reported build times 75% faster after removing barrel files. In a large JavaScript module system architecture these convenience files build dependency chains that no bundler can shake out. I import core components directly and keep barrel files for small, cohesive utility sets.
If this JavaScript module system architecture stuff is eating your dev hours, I can take it on. I have been wrestling with WordPress and messy JS environments since the 4.x days.
What to do about it
Architecture is the boundaries between your files rather than the folders you sort them into. Use ESM so the tooling can analyze what you wrote. Keep the dependency rule strict enough that your core logic stays free of framework details. Check the module graph now and then, and cut circular dependencies while they are still small.
