Prev Next

How JavaScript Works

JavaScript is a high-level, single-threaded, interpreted language. It uses a combination of the browser's JavaScript engine, an event loop, and a call stack to execute code. Understanding how JavaScript works is essential for writing efficient and optimized code.

Key Topics

JavaScript Engine

The JavaScript engine (e.g., V8 for Chrome) is responsible for interpreting and executing JavaScript code. It converts human-readable code into machine code and runs it efficiently. The engine uses techniques like Just-In-Time (JIT) compilation for optimization.

Call Stack

The call stack is a data structure that keeps track of function execution. When a function is invoked, it is pushed onto the stack. When the function execution completes, it is popped off the stack. This process helps JavaScript keep track of the order of function calls.

function firstFunction() {
    console.log("First Function Start");
    secondFunction();
    console.log("First Function End");
}

function secondFunction() {
    console.log("Second Function");
}

firstFunction();

Output

First Function Start

Second Function

First Function End

Explanation: The call stack first pushes firstFunction onto the stack. When secondFunction is called, it is added to the stack. Once secondFunction completes, it is removed, and the execution continues in firstFunction.

Event Loop

The event loop is a mechanism that ensures non-blocking asynchronous operations in JavaScript. It continuously monitors the call stack and the task queue, transferring tasks to the stack when it is empty.

console.log("Start");

setTimeout(() => {
    console.log("Async Task");
}, 1000);

console.log("End");

Output

Start

End

Async Task

Explanation: The synchronous tasks Start and End are executed first. The asynchronous task from setTimeout is added to the task queue and executed after the specified delay once the call stack is empty.

DOM Interaction Example

JavaScript handles asynchronous tasks efficiently using the event loop. This can be observed in DOM manipulation examples where user interactions trigger events dynamically.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Event Loop Example</title>
</head>
<body>
    <button id="btnClick">Click Me</button>
    <script>
        document.getElementById("btnClick").addEventListener("click", () => {
            console.log("Button clicked");
        });
        console.log("Script Loaded");
    </script>
</body>
</html>

Explanation: The button click event is added to the event loop's task queue. Once the script execution completes, the event listener is executed when the button is clicked.

Key Takeaways

  • JavaScript Engine: Executes JavaScript code using JIT compilation for optimization.
  • Call Stack: Tracks the order of function execution.
  • Event Loop: Manages asynchronous operations and ensures smooth execution.
Prev Next