16. What is the difference between let and var?

The difference between let and var in JavaScript mainly lies in scope, hoisting, and re-declaration.

Key Differences:

1. Scope:

   • var is function-scoped (accessible throughout the function).
   • let is block-scoped (accessible only within {} where it is defined).

2. Hoisting:

   • var is hoisted and initialized as undefined.
   • let is hoisted but not initialized (using it before declaration gives a ReferenceError).

3. Re-declaration:

   • var can be re-declared within the same scope.
   • let cannot be re-declared within the same scope.

Example:

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function test() {
    if (true) {
        var x = 10;  // Function-scoped
        let y = 20;  // Block-scoped
    }
    console.log(x); // ✅ Works (var is accessible)
    console.log(y); // ❌ Error (let is block-scoped)
}
test();

Hoisting Example:

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console.log(a); // ✅ Output: undefined (var is hoisted)
var a = 5;

console.log(b); // ❌ ReferenceError (let is not initialized)
let b = 10;

Conclusion:

• Use let to avoid unexpected behavior due to var's function-scoping and hoisting.
• Prefer let over var in modern JavaScript. 🚀