https://github.com/callmeskyy111/nodejs-resources

All resources related to NodeJs/ExpressJs development ✅
https://github.com/callmeskyy111/nodejs-resources

asynchronous-programming ejs express graphql javascript jsonwebtoken mongodb mongoose mongoose-schema node-modules node-typescript nodejs npm rest-api socket-io

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All resources related to NodeJs/ExpressJs development ✅

Host: GitHub
URL: https://github.com/callmeskyy111/nodejs-resources
Owner: callmeskyy111
Created: 2025-01-28T18:15:35.000Z (4 months ago)
Default Branch: main
Last Pushed: 2025-01-28T18:41:44.000Z (4 months ago)
Last Synced: 2025-03-05T22:48:51.566Z (3 months ago)
Topics: asynchronous-programming, ejs, express, graphql, javascript, jsonwebtoken, mongodb, mongoose, mongoose-schema, node-modules, node-typescript, nodejs, npm, rest-api, socket-io
Language: JavaScript
Homepage:
Size: 232 KB
Stars: 0
Watchers: 1
Forks: 0
Open Issues: 0
Metadata Files:
- Readme: README.md

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README

Node.js is a **runtime environment** for executing JavaScript outside of a web browser. Built on **Chrome's V8 JavaScript engine**, Node.js is designed for building scalable and high-performance applications using a **non-blocking, event-driven architecture**. Here's an in-depth look at how Node.js works under the hood:

---

### **1. Components of Node.js**

#### **1.1 V8 Engine**
- Node.js uses the **V8 engine** (developed by Google) to execute JavaScript code.
- V8 compiles JavaScript into **machine code** for fast execution.

#### **1.2 libuv**
- A **C library** that provides Node.js with its **event-driven, non-blocking I/O model**.
- Manages the **Event Loop**, **thread pool**, and **asynchronous operations** like file I/O, network requests, and timers.

#### **1.3 Event Loop**
- The **heart** of Node.js.
- A single-threaded loop that manages asynchronous operations and their callbacks.

#### **1.4 C++ Bindings**
- Node.js uses C++ bindings to access **low-level system resources** (e.g., file systems, networking, etc.) and expose these functionalities to JavaScript APIs.

---

### **2. Core Concepts of Node.js Architecture**

#### **2.1 Single-Threaded**
- Node.js operates on a **single-threaded** model for processing JavaScript code.
- Handles concurrency through **non-blocking I/O** and **libuv's thread pool**.

#### **2.2 Non-Blocking I/O**
- Asynchronous APIs allow tasks like database queries or file reads to run in the background while the main thread continues executing other code.

#### **2.3 Event-Driven**
- Node.js uses an **event-driven model** where asynchronous events are queued, and their callbacks are executed by the Event Loop.

#### **2.4 Asynchronous Execution**
- Node.js defers blocking operations (e.g., file I/O) to **libuv's thread pool** and returns control to the Event Loop.

---

### **3. Node.js Workflow (Under the Hood)**

#### **Step 1: Input (JavaScript Code Execution)**
- The developer writes JavaScript code.
- The **V8 engine** compiles and executes this JavaScript code.

#### **Step 2: Event Loop**
- The **Event Loop** manages the execution of code, collecting and processing events, and delegating tasks.
- Tasks include timers, I/O operations, and callbacks.

#### **Step 3: Libuv and Thread Pool**
- For CPU-bound or blocking operations, tasks are handed to libuv's **thread pool** (4 threads by default).
- Examples: File reading, database queries, DNS lookups.

#### **Step 4: OS Interaction**
- libuv uses system-specific features (e.g., `epoll`, `kqueue`, `IOCP`) to efficiently perform non-blocking I/O.

#### **Step 5: Callback Execution**
- Once a task completes (e.g., a file is read), the callback is queued in the Event Loop.
- The callback is executed when the Event Loop processes it.

---

### **4. Event Loop in Detail**

The Event Loop has multiple phases, executed in a specific order:

#### **4.1 Timers Phase**
- Executes callbacks scheduled by `setTimeout` and `setInterval`.

#### **4.2 Pending Callbacks Phase**
- Executes I/O callbacks deferred by certain operations (e.g., DNS resolution).

#### **4.3 Idle/Prepare Phase**
- Internal operations of Node.js (used rarely).

#### **4.4 Poll Phase**
- Retrieves new I/O events and executes their callbacks.

#### **4.5 Check Phase**
- Executes callbacks from `setImmediate`.

#### **4.6 Close Callbacks Phase**
- Executes callbacks for closed connections or resources.

---

### **5. Workflow Diagram**

---

### **6. Example Code: Node.js in Action**

```javascript
const fs = require("fs");

console.log("Start");

// Asynchronous file read
fs.readFile("example.txt", "utf8", (err, data) => {
if (err) throw err;
console.log("File content:", data);
});

setTimeout(() => {
console.log("Timer completed");
}, 1000);

console.log("End");
```

#### **Execution Flow**:
1. **`Start`** is logged (synchronous).
2. `fs.readFile` begins, libuv delegates it to the thread pool.
3. **`End`** is logged (synchronous).
4. Timer (`setTimeout`) callback is queued in the Event Loop.
5. Once the file is read, the `fs.readFile` callback is queued.
6. Both callbacks are executed in order.

---

### **7. Advantages of Node.js Architecture**
- **Scalable**: Handles thousands of concurrent connections efficiently.
- **Fast**: Non-blocking I/O and V8 engine make Node.js highly performant.
- **Cross-Platform**: Works seamlessly on Windows, macOS, and Linux.

---

### **8. Summary**
- Node.js combines **V8**, **libuv**, and a **single-threaded Event Loop** to handle asynchronous, non-blocking tasks.
- Tasks are managed by the Event Loop, while libuv’s thread pool takes care of blocking operations.
- This architecture makes Node.js suitable for **real-time, scalable applications**, such as chat servers, streaming platforms, and APIs.

![image](https://github.com/user-attachments/assets/20213f49-3af3-4db7-86f0-654e91469e9c)
### **What is the Event Loop?**

The Event Loop is a core mechanism in JavaScript that handles asynchronous operations. It enables JavaScript to be **non-blocking** and **single-threaded** by delegating tasks (e.g., I/O operations, timers, or network requests) to the system and managing their execution without blocking the main thread.

In the context of **Node.js**, the Event Loop is what allows Node.js to perform non-blocking I/O operations by offloading tasks to the underlying operating system, while continuing to execute other code.

---

### **How Does the Event Loop Work in Node.js?**

Node.js runs on a single thread, but it uses an **event-driven architecture** where I/O operations are handled by the **libuv library**. This library provides the Event Loop and a thread pool for managing asynchronous tasks.

The Event Loop continuously monitors the **call stack**, **callback queue**, and **task sources** to determine what code to execute next.

---

### **Phases of the Event Loop**

The Event Loop in Node.js operates in a sequence of phases. Each phase has a specific task and executes callbacks in a First In, First Out (FIFO) order. The main phases are:

#### 1. **Timers Phase**
- Executes callbacks scheduled by `setTimeout` and `setInterval`.
- It checks for expired timers and executes their corresponding callbacks.

#### 2. **I/O Callbacks Phase**
- Executes callbacks for deferred I/O operations, such as file reading, network requests, or database queries.

#### 3. **Idle, Prepare Phase**
- Internal phase used for system-level operations, often ignored in user code.

#### 4. **Poll Phase**
- Handles new incoming I/O events (e.g., data from a file or network).
- Executes I/O-related callbacks as long as there are events in the queue.
- If no tasks are queued, the Event Loop will wait for new tasks.

#### 5. **Check Phase**
- Executes callbacks registered by `setImmediate`.
- `setImmediate` callbacks are always executed after the Poll phase.

#### 6. **Close Callbacks Phase**
- Executes callbacks for events such as `close` (e.g., `socket.on('close')`).

---

### **How It All Fits Together**

1. **Call Stack**:
- Contains the code currently being executed.
- If the stack is empty, the Event Loop picks the next task from the appropriate queue.

2. **Queues**:
- **Callback Queue**: Holds tasks like `setTimeout` and I/O callbacks.
- **Microtask Queue**: Holds `Promises` (via `.then`) and `process.nextTick`. Microtasks are prioritized over tasks in the Callback Queue.

3. **Execution Order**:
- The Event Loop processes all the Microtasks in the Microtask Queue before moving to the next phase.
- Tasks like `setTimeout` and `setImmediate` are placed in the Callback Queue and executed in the corresponding phase.

---

### **Code Example**

```javascript
console.log("Start");

setTimeout(() => {
console.log("Timeout callback");
}, 0);

setImmediate(() => {
console.log("Immediate callback");
});

Promise.resolve().then(() => {
console.log("Promise resolved");
});

process.nextTick(() => {
console.log("Next Tick");
});

console.log("End");
```

#### **Execution Order**:
1. `Start` and `End` (synchronous code executes first).
2. `process.nextTick` (nextTick microtasks are executed before promises).
3. `Promise resolved` (Microtask Queue).
4. `Timeout callback` (Timers Phase).
5. `Immediate callback` (Check Phase).

---

### **Why is the Event Loop Important in Node.js?**

1. **Non-Blocking I/O:**
- Allows Node.js to handle thousands of concurrent connections without blocking the main thread.

2. **Scalability:**
- Makes Node.js efficient for I/O-heavy tasks like APIs, file systems, and real-time applications.

3. **Single-Threaded Simplicity:**
- Developers don’t need to deal with the complexity of threads or locks.

---

### **Key Points to Remember**
- Node.js is single-threaded, but the Event Loop leverages asynchronous callbacks and a thread pool (via libuv).
- `process.nextTick` and Promises (Microtasks) have higher priority than `setTimeout` and `setImmediate`.
- The Event Loop phases execute in a consistent order, ensuring predictable behavior.

Understanding the Event Loop is crucial for writing performant and efficient asynchronous code in Node.js!
### **What is libuv?**

**libuv** is a multi-platform C library that provides support for asynchronous I/O operations. It is a key component of **Node.js** and powers its **event-driven, non-blocking architecture**. Essentially, libuv acts as the backbone for handling low-level operating system tasks such as file I/O, networking, timers, and more, enabling Node.js to achieve high performance and scalability.

---

### **Why is libuv Important in Node.js?**

Node.js is **single-threaded** but highly efficient in managing concurrent tasks. This is made possible by libuv, which handles:

1. **Non-blocking I/O**: Manages asynchronous operations like reading/writing files, making network requests, and interacting with databases.
2. **Thread Pool**: Delegates CPU-intensive operations to a thread pool, ensuring the main thread remains free for other tasks.
3. **Cross-Platform Abstraction**: Provides a consistent API for working with the operating system across platforms (e.g., Windows, Linux, macOS).

---

### **Key Features of libuv**

1. **Event Loop**:
- The core of libuv is the **Event Loop**, which schedules and executes asynchronous callbacks.
- It follows a predictable cycle of phases to manage events like timers, I/O, and system-level tasks.

2. **Thread Pool**:
- libuv uses a **thread pool** (default size: 4 threads) for executing blocking or CPU-bound operations, such as:
- File system tasks (`fs.readFile`, etc.).
- Compression and cryptography operations.
- The results of these tasks are returned asynchronously.

3. **Asynchronous I/O**:
- Provides non-blocking APIs for networking, file systems, and DNS resolution.

4. **Timers**:
- Implements timers (`setTimeout`, `setInterval`) using high-performance mechanisms like `uv_timer`.

5. **Cross-Platform Support**:
- Abstracts platform-specific details, such as Windows IOCP (I/O Completion Ports) and Linux epoll/kqueue, to offer a unified API.

6. **Other Utilities**:
- Provides utilities for:
- TCP and UDP sockets.
- Child processes.
- Signal handling.
- File and directory watching.

---

### **How Does libuv Work?**

1. **Event Loop Execution**:
The Event Loop in libuv manages different phases like timers, I/O callbacks, and polling. It ensures tasks are processed efficiently.

2. **Delegating Tasks**:
Tasks that are asynchronous or blocking are handed off to the thread pool. Once completed, the results are pushed back into the Event Loop.

3. **Platform-Specific Handling**:
libuv uses OS-specific features for efficient task management:
- On **Linux**, it uses `epoll`.
- On **macOS**, it uses `kqueue`.
- On **Windows**, it uses `IOCP`.

---

### **Diagram of libuv in Node.js**

```plaintext
+-------------------+
| Your Node.js |
| Application |
+-------------------+
|
v
+-----------------------------+
| Node.js Runtime |
+-----------------------------+
|
v
+----------------+
| libuv |
+----------------+
/ | \ \
Timers Thread Pool Network File I/O
```

---

### **libuv in Action: Example Code**

```javascript
const fs = require('fs');

console.log('Start');

// Asynchronous File Read (handled by libuv's thread pool)
fs.readFile('example.txt', (err, data) => {
if (err) throw err;
console.log('File read complete:', data.toString());
});

setTimeout(() => {
console.log('Timer complete');
}, 0);

console.log('End');
```

#### **Execution Flow**:
1. `Start` is logged (synchronous).
2. `fs.readFile` delegates file reading to libuv’s thread pool.
3. `End` is logged (synchronous).
4. Timer callback is added to the Event Loop queue and executes after synchronous code.
5. Once the file reading is complete, its callback is added to the Event Loop queue and executed.

---

### **Summary**

- **libuv** is the core library enabling Node.js to handle asynchronous tasks.
- It provides an abstraction over OS-level features, enabling cross-platform compatibility.
- Its primary responsibilities include managing the Event Loop, thread pool, non-blocking I/O, and timers.
- By offloading tasks from the main thread, libuv allows Node.js to be efficient and scalable, even with a single-threaded architecture.

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