The .cjs file extension is used for JavaScript files that contain code written using the CommonJS module system. CommonJS is a module format designed primarily for use outside of web browsers, such as in Node.js environments. These files encapsulate JavaScript code into reusable modules, allowing developers to organize their code into logical units and manage dependencies effectively. Unlike ES modules (.mjs), CommonJS modules use require() to import dependencies and module.exports (or exports) to expose functionality to other modules. This system allows for modularity and code reuse, making it easier to manage large JavaScript projects. The .cjs extension explicitly signals to JavaScript runtimes and build tools that the file should be treated as a CommonJS module, ensuring that the correct module loading mechanism is used. This is particularly important in environments where both CommonJS and ES modules are supported, as it avoids ambiguity and ensures consistent behavior. Using .cjs helps maintain compatibility with older Node.js projects and tools that rely on the CommonJS module system.