Introduction to Node.js Asynchronous Programming: Callback Functions and Promise Basics

Node.js, due to JavaScript's single-threaded nature, requires asynchronous programming to handle high-concurrency I/O operations (such as file reading and network requests). Otherwise, synchronous operations will block the main thread, leading to poor performance. The core of asynchronous programming is to ensure that time-consuming operations do not block the main thread and that results are notified via callbacks or Promises upon completion. Callback functions were the foundation of early asynchronous programming. For example, the callback of `fs.readFile` receives `err` and `data`, which is simple and intuitive but prone to "callback hell" (with deep nesting and poor readability). Error handling requires repetitive `if (err)` checks. Promises address callback hell by being created with `new Promise`, having states: pending (in progress), fulfilled (success), and rejected (failure). They enable linear and readable asynchronous code through `.then()` chaining and centralized error handling with `.catch()`, laying the groundwork for subsequent `async/await`. Core Value: Callback functions are foundational, Promises enhance readability, and asynchronous thinking is key to building efficient Node.js programs.