Types of Variable

Variable Type	Scope	Reassignment	Redeclaration
var	Function	✅ Yes	✅ Yes
let	Block	✅ Yes	❌ No
const	Block	❌ No	❌ No

1. var (Introduced in ES3 - 1999)

✅ Strengths:

• Can be redeclared and reassigned.
• Function-scoped (accessible within the function where it's declared).
• Hoisted (moved to the top of the scope).

❌ Limitations:

• Not block-scoped, meaning it can be accessed outside {} blocks.
• Can cause unintended bugs due to accidental redeclaration.

Example

var x = 10;
if (true) {
  var x = 20; // Redeclaring allowed
}
console.log(x); // 20 (Not block-scoped)

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2. let (Introduced in ES6 - 2015)

✅ Strengths:

• Block-scoped (only accessible inside {} where declared).
• Can be reassigned but not redeclared in the same scope.
• Prevents hoisting-related issues.

❌ Limitations:

• Cannot be redeclared within the same block.

Example

let y = 10;
if (true) {
  let y = 20; // This `y` is different (block-scoped)
  console.log(y); // 20
}
console.log(y); // 10 (Original `y` remains unchanged)

---

3. const (Introduced in ES6 - 2015)

✅ Strengths:

• Block-scoped like let.
• Cannot be reassigned after declaration.
• Ensures immutability (useful for constants, objects, arrays).

❌ Limitations:

• Must be assigned a value when declared.
• The reference cannot be changed, but objects/arrays can be modified.

Example

const z = 30;
// z = 40;  // ❌ Error: Cannot reassign a `const` variable

const arr = [1, 2, 3];
arr.push(4); // ✅ Allowed, modifying array contents
console.log(arr); // [1, 2, 3, 4]