Application scenarios of Node.js

Node.js, a JavaScript runtime environment based on the Chrome V8 engine, is renowned for its non-blocking I/O and event-driven characteristics, making it suitable for high-concurrency, low-latency scenarios. Typical applications include real-time applications like chat rooms (implementing bidirectional communication via WebSocket), API services and microservice architectures (quickly building backend services with Express), server-side rendering (improving first-screen loading speed), and command-line tool development (processing files or automation scripts). It is also used in IoT applications (connecting sensors and handling data streams), efficiently processing large files, middleware services (aggregating interfaces and transforming data formats), cloud functions (supporting event-driven serverless functions), proxy servers (implementing request forwarding), and database operations (supporting mainstream databases like MongoDB and MySQL). It is ideal for rapid development of data-intensive applications.

The CommonJS module system translates this sentence into English.

The CommonJS module system is the core mechanism for organizing and managing code in Node.js, enabling module import and export through `require` and `module.exports`. It addresses the lack of native modular support in early JavaScript. Each file is treated as an independent module, with variables, functions, and classes inside the module being private by default and requiring explicit export for external access. Key features of the module system include synchronous loading, a caching mechanism, clear dependencies, and simple syntax. Exports can be done via `module.exports` or the `exports` shorthand, while imports use the `require` function, which follows specific lookup rules covering core modules, file modules, directory modules, and `node_modules` modules. The caching mechanism handles circular dependencies, and each module has an isolated scope to avoid polluting the global environment. Although primarily synchronous, dynamic loading is also possible. Differences exist between CommonJS and ES modules, such as loading methods and syntax. Practical applications include configuration file management, middleware patterns, and support for various module organization modes like singletons and factories. It also involves module version management and testing techniques.

Single-threaded and event loop

Node.js adopts a single-threaded model for executing JavaScript code, simplifying the concurrency model but introducing performance bottlenecks. The event loop is key to achieving non-blocking I/O by delegating I/O operations to the system kernel via the libuv library. Tasks are categorized into microtasks and macrotasks, with microtasks having higher priority. CPU-intensive tasks can block the event loop and should be handled using worker threads. Performance monitoring interfaces are provided to detect event loop latency. In web servers, CPU-intensive routes should use worker threads, while I/O-intensive ones can be processed directly. Advanced patterns leverage event loop features for traffic control, such as rate limiter classes.

The non-blocking I/O model

Node.js's non-blocking I/O model is its core feature, enabling efficient handling of a large number of concurrent requests. Unlike traditional blocking I/O, it does not wait for I/O operations to complete but continues executing subsequent code, processing results through callback functions. The event loop mechanism is key to implementing this feature, consisting of multiple phases such as timers, I/O callbacks, and polling. While it improves performance, it may lead to callback hell, which can be resolved using Promises and async/await. Non-blocking I/O is suitable for scenarios like HTTP servers and database operations but not ideal for CPU-intensive tasks. Attention must be paid to error handling and memory usage. Stream processing is an advanced application suitable for large files, while worker threads can handle CPU tasks. Debugging asynchronous code can be done using the async_hooks module. Best practices include avoiding blocking the event loop, using Promises wisely, error handling, stream processing, and concurrency control.

Event-driven architecture

Event-Driven Architecture (EDA) is a software design pattern centered around events, where system components communicate by producing and consuming events. Node.js is inherently well-suited for implementing EDA, with its core `events` module providing the `EventEmitter` class as a foundation. The event loop mechanism includes phases such as timers, pending callbacks, polling, and checks. The `EventEmitter` class offers rich methods for managing event listeners, and common design patterns include simple event handling, event aggregators, event buses, and the publish-subscribe pattern. In web applications, it can decouple components, such as in user registration workflows. Special attention should be paid to error handling, avoiding memory leaks, and controlling the number of listeners. In microservices environments, it enables loose coupling and can be combined with Event Sourcing and CQRS patterns. During testing, the asynchronous nature must be considered.

The definition and characteristics of Node.js

Node.js is a JavaScript runtime environment based on the Chrome V8 engine, enabling JavaScript for server-side development. Its event-driven and non-blocking I/O model makes it particularly suitable for building high-performance network applications. It employs a single-threaded event loop mechanism to handle high concurrency and boasts a rich npm module ecosystem. Supporting cross-platform operation, it is ideal for real-time applications, API services, microservices, and data stream processing. It implements modularity via CommonJS and supports ES modules. Performance can be optimized using cluster mode. Promises or async/await are recommended to avoid callback hell. It provides a built-in debugger and supports testing frameworks like Mocha and Jest.