To truly understand asynchronous JavaScript, we need to look at how JavaScript handles execution behind the scenes using the Call Stack, Web APIs, Callback Queue, and Event Loop.

JavaScript Execution Model 🛠️

JavaScript is single-threaded, meaning it executes one task at a time. However, using asynchronous features (like setTimeout, Promises, and fetch API), JavaScript can handle multiple tasks without blocking the main thread.

Let's break this down step by step. 🧐

1️⃣ Call Stack – The Heart of Execution ❤️

📌 The Call Stack is a LIFO (Last In, First Out) data structure where JavaScript keeps track of function calls.

🔹 Example: Call Stack in Action

function greet() {
    console.log("Hello!");
}

function welcome() {
    greet();
    console.log("Welcome!");
}

welcome();

🔍 How It Executes in the Call Stack:

1️⃣ welcome() is called → Pushed to the stack

2️⃣ Inside welcome(), greet() is called → Pushed to the stack

3️⃣ console.log("Hello!") executes → Removed from the stack

4️⃣ greet() completes → Removed from the stack

5️⃣ console.log("Welcome!") executes → Removed from the stack

6️⃣ welcome() completes → Removed from the stack

🛑 Problem: The Call Stack executes tasks synchronously (one at a time). If a function takes too long, it blocks other code from running.