Variables

The variables are declared in JS using three keywords:

• var: Older way to declare variables.
• let: It allows for block-scoping and is commonly used for mutable variables.
• const: It declares a constant variable whose value cannot be re-assigned. It's commonly used for immutable values.

let, const are preferred as they provide better scoping

Example:

// Using var
var age = 19;
// Using let
let name = "DevDuo";
// Using const
const PI = 3.14;

Variable Scope:

• Global Scope: Variables declared outside any function or block have global scope and can be accessed throughout the entire program.

let globalVar = "I am global";

function exampleFunction() {
  console.log(globalVar); // Accessible inside the function
}
exampleFunction();
console.log(globalVar);    // Accessible outside the function

• Local (Function) Scope: Variables declared inside a function have local scope and are only accessible within that function.

function localExample() {
  let localVar = "I am local";
  console.log(localVar);   // Accessible inside the function
}

localExample();
// console.log(localVar);  // This would result in an error; localVar is not accessible outside the function

• Block Scope (let and const): Variables declared with let and const are block-scoped, meaning they are only accessible within the block (enclosed by curly braces) where they are declared.

if (true) {
  let blockVar = "I am block-scoped";
  console.log(blockVar);   // Accessible inside the block
}
// console.log(blockVar);  // This would result in an error; blockVar is not accessible outside the block