NODE面試問題...

1. What is Node.js?

Answer: Node.js is a runtime environment built on Chrome's V8 JavaScript engine that allows developers to run JavaScript code on the server side. It's designed for building scalable network applications and supports non-blocking, event-driven architecture.

2. What is the difference between Node.js and JavaScript?

Answer: JavaScript is a programming language that runs in the browser.
Node.js is a runtime environment that allows JavaScript to run on the server side.

3. What is Event-Driven Programming in Node.js?

Answer: Event-driven programming is a programming paradigm where the flow of the program is determined by events such as user actions, sensor outputs, or messages from other programs. In Node.js, event-driven programming is central to handling asynchronous operations using event emitters and listeners.

4. What is the difference between process.nextTick() and setImmediate()?

Answer: process.nextTick() schedules a callback to execute after the current operation completes, but before the event loop continues.
setImmediate() schedules a callback to be placed on the event loop after I/O events.

5. How does Node.js handle asynchronous operations?

Answer: Node.js uses a single-threaded, non-blocking I/O model with event-driven architecture. It leverages callbacks, promises, and async/await to handle asynchronous operations, ensuring that the server can process many requests concurrently without blocking the main thread.

6. What are streams in Node.js?

Answer: Streams are objects in Node.js that let you read or write data in chunks. They are used to handle large volumes of data by processing it in smaller, manageable chunks, which reduces memory usage. There are four types of streams:

Readable (e.g., fs.createReadStream())
Writable (e.g., fs.createWriteStream())
Duplex (both readable and writable)
Transform (a type of duplex stream where the output is a transformation of the input)

7. What is the difference between synchronous and asynchronous code in Node.js?

Answer: Synchronous code is blocking; it waits for each operation to complete before moving to the next.
Asynchronous code is non-blocking; it allows the program to continue executing without waiting for the operation to complete (handled via callbacks, promises, or async/await).

8. What are middleware functions in Express.js?

Answer: Middleware functions in Express.js are functions that execute during the request-response cycle. They can modify the request, response, or execute some logic before passing control to the next middleware function. Common types include:

Application-level middleware: Bound to an instance of express()
Router-level middleware: Bound to an instance of express.Router()
Error-handling middleware

9. How does the event loop work in Node.js?

*Answer: * The event loop is responsible for handling asynchronous callbacks in Node.js. It continuously monitors the call stack, the task queue, and the I/O operations. When the call stack is empty, it processes the tasks from the event queue, ensuring non-blocking I/O by deferring heavy operations.

10. What is the use of the cluster module in Node.js?

Answer: The cluster module allows Node.js to create child processes (workers) that share the same server port. This helps in load balancing and making full use of multi-core systems by running multiple instances of Node.js to handle more requests simultaneously.

11. What is the difference between require() and import in Node.js?

Answer: require() is part of the CommonJS module system and is synchronous. It's used to load modules in versions of Node.js before ES6.
import is part of the ES6 module system, and it works with JavaScript’s native module system, enabling support for tree-shaking and static analysis. It's used in newer versions of Node.js with ECMAScript modules.

12. How do you handle errors in Node.js?

Answer: Error handling can be done in several ways:

Using callbacks with the error-first pattern (callback(err, result))
Using Promises with .catch() for rejected promises
Using try...catch blocks with async/await
Using middleware in Express.js for handling errors

13. package.json 檔案的用途是什麼？

答案： package.json 是 Node.js 專案中的清單文件，其中包含有關項目及其相依性的元資料。它定義了專案的名稱、版本、主入口點、腳本、依賴項、devDependency 和其他配置。

1. 如何保護 Node.js 應用程式的安全性？ 答案： 使用 HTTPS 進行安全通訊。 實施資料驗證和清理以防止 SQL 注入和跨站點腳本 (XSS)。 使用強大的身份驗證和授權機制（例如 JWT）。 使用環境變數和安全性儲存來保護敏感資料。 透過速率限制和超時來防止 DOS 攻擊。 保持您的軟體包更新並使用 npmaudit 等審核工具。

15. fs.readFile() 和 fs.createReadStream() 有什麼不同？

*答案：* fs.readFile() 將整個檔案讀取到記憶體中，然後使用檔案內容執行回呼。
fs.createReadStream() 以區塊的形式讀取文件，這使得大文件的記憶體效率更高，因為它串流資料而不是一次性載入全部資料。

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