JavaScript Basics: Developer Console, Data Types, Variables, and Essential Functions

JavaScript Fundamentals Guide

📚 Table of Contents

• Developer Console
• Data Types
• Variables (var)
• Common Functions
• Live Code Playground
• Interactive Quiz
• Key Takeaways
• Related Articles

1. JavaScript Developer Console

The Developer Console allows you to run JavaScript directly in your browser for testing and debugging.

📖 Learn More

Use it to test code instantly without creating files.

💻 Code Example

console.log("Hello, World!");

🖥 CLI Output

> Hello, World!

2. JavaScript Data Types

Primitive data types are the building blocks of JavaScript.

📖 View Data Types

• String: "Hello"
• Number: 42
• Boolean: true / false
• Undefined: let x;
• Null: let y = null;

💻 Code Example

var text = "Hello";
var num = 10;
var isTrue = true;

🖥 CLI Output

> Hello
> 10
> true

3. Variables using var

The var keyword declares variables but has hoisting behavior.

📖 Hoisting Explained

Variables declared with var are moved to the top and initialized as undefined.

💻 Code Example

console.log(name);
var name = "Bob";

🖥 CLI Output

> undefined

4. Common JavaScript Functions

📖 console.log()

Used for debugging.

console.log("Hello!");

📖 alert()

Displays popup messages.

alert("Welcome!");

📖 prompt()

Takes user input.

var user = prompt("Enter name");

🖥 CLI Output

> Hello!
> Welcome!
> User Input

🧪 Live Code Playground

Try JavaScript directly below:

console.log("Try editing this code!");

🧠 Interactive Quiz

1. What is the output of console.log(typeof null)?

2. Which keyword has block scope?

💡 Key Takeaways

• Console helps test code quickly
• Primitive types are core building blocks
• var has hoisting behavior
• Functions help debugging and interaction

🔗 Related Articles

• Essential DOM Methods for Accessing HTML Elements