Understanding Local and Global Variables in JavaScript

Global Variables

Declared outside any function, global variables can be accessed and modified from anywhere in the program.

let message = "Hello"; // global

function greet() {
    console.log(message); // accessible here
}

Local Variables

Declared inside a function or block, local variables are only accessible within that function or block.

function greet() {
    let message = "Hi"; // local
    console.log(message);
}
console.log(message); // Error: message is not defined

Why Scope Matters

Keeping variables local wherever possible avoids naming conflicts and makes code easier to reason about and debug.