The evolution of managing code in JavaScript has been a long journey, marked by various approaches and persistent challenges. For many years, developers relied on simple <script> tags embedded directly in HTML pages. This approach was straightforward for small projects, but it quickly led to significant issues as applications grew larger and more complex.
The primary problem was the global scope. Every script executed in the same shared environment, meaning variables and functions from one script could easily conflict with those from another. Dependencies between scripts had to be managed manually by ensuring the correct order of inclusion in the HTML. This became unwieldy, error-prone, and difficult to maintain, especially in larger teams or open-source projects. Code reusability was low, and understanding the flow of an application became increasingly complicated.
The need for better organization and managing dependencies became clear. This led to the development of various solutions outside the core JavaScript language itself. On the server side, specifically with the rise of Node.js, CommonJS emerged as a popular module system. It used require() and module.exports to define and import modules, providing a synchronous loading mechanism suitable for server environments where files are readily available.
However, CommonJS wasn’t directly suitable for browsers. Synchronous loading would block the main thread, freezing the user interface while scripts were fetched over the network. This limitation prompted the creation of module systems designed for the browser’s asynchronous nature. AMD (Asynchronous Module Definition), notably implemented by RequireJS, allowed defining modules and their dependencies asynchronously using a define() function. This prevented blocking and improved performance for browser-based applications.
The existence of different module systems for the server (CommonJS) and browser (AMD) created a new challenge: interoperability. Developers often had to write code that could work in both environments or use build tools to transform code between systems. This led to the development of UMD (Universal Module Definition), a pattern designed to create modules that could be consumed by either CommonJS or AMD loaders, or even work with the old global scope if no loader was present. While UMD offered compatibility, it added complexity to module definitions.
The ultimate goal was a native, standard module system built into the JavaScript language itself that could work uniformly across different environments. This arrived with ES Modules (ESM), introduced in ECMAScript 2015 (ES6). ESM uses import and export keywords, providing a declarative syntax for defining and using modules. It supports both static analysis (allowing tools to understand dependencies without execution) and the potential for efficient, asynchronous loading.
Despite ESM being the standard, the transition hasn’t been without its hurdles. One major challenge has been browser and Node.js support rollout. While modern environments support ESM, older versions still exist, requiring developers to use build tools like Webpack or Parcel to transpile their code and manage compatibility. Interoperability with existing CommonJS modules in the Node.js ecosystem also presented difficulties, leading to various approaches and ongoing refinements in how ESM and CommonJS interact.
Tooling support has been crucial. Build tools, bundlers, and package managers had to evolve to fully support ESM‘s features, including handling dependencies, tree-shaking (removing unused code), and code splitting for better performance. Migrating existing projects built with older module systems to ESM can also be a complex process, requiring careful planning and refactoring.
Today, ES Modules are the recommended standard for new JavaScript development, offering a robust and efficient way to organize code and manage dependencies. While challenges related to legacy code, ecosystem interoperability, and tooling complexity persist, the industry is steadily moving towards a more unified and standardized approach to JavaScript modules, a significant step forward from the days of scattered <script> tags and global scope chaos.
Source: https://itnext.io/modules-in-javascript-a-20-year-mistake-729b75347580?source=rss—-5b301f10ddcd—4
