What is JavaScript's Core Nature?

JavaScript is single-threaded - imagine a single worker who can only do ONE task at a time.

console.log("Task 1");
console.log("Task 2");
console.log("Task 3");
// Executes line by line, top to bottom

The Problem: Blocking Operations

Some operations take time:

• Making API calls (network requests)
• Reading files
• Database queries
• Timers

If JavaScript waits for these, everything freezes:

// ❌ BAD - Everything stops here
let data = waitForAPI();  // Blocks for 3 seconds
console.log(data);
console.log("This waits 3 seconds too!");

The Solution: Asynchronous Programming

Don't wait - instead, say "Call me back when you're done":

// ✅ GOOD - Non-blocking
fetchAPI(function() {
    console.log("Data received!");
});
console.log("I run immediately!");

// Output:
// I run immediately!
// Data received!  (after delay)

This "call me back" function is a CALLBACK.

📦 Real-World Analogy

Think of ordering food online:

1. Place order → Wait → Get order ID