7. Variables: The Legacy var Keyword

A variable is essentially a container for storing data values. Before 2015, var was the only way to declare variables.

Declaring and Initializing

javascript var message = 'Hello World'; // Declaration and initialization var count; // Declaration only (value is undefined) count = 50;

console.log(message); // Output: Hello World

Variable Reassignment

You can change the value of a var variable at any time.

javascript var score = 100; score = 150; // Reassigned console.log(score); // Output: 150

The Scope Problem with var

var is function-scoped, meaning it is visible throughout the function it is defined in, ignoring block structures like if statements or for loops.

javascript function example() { if (true) { var greeting = 'Hi'; } console.log(greeting); // Output: Hi (This is unexpected behavior!) }

Due to this scoping issue, modern JS prefers let and const.