Q93- What is the difference between let, const, and var?

var, let, and const are used to declare variables in JavaScript, but they differ in scope, hoisting, and mutability.

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1️⃣ var

• Scope: Function-scoped
• Hoisting: Yes, initialized with undefined
• Reassignable: Yes
• Redeclarable: Yes

function exampleVar() {
  if (true) {
    var x = 10;
  }
  console.log(x); // 10 → accessible outside block
}
exampleVar();

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2️⃣ let

• Scope: Block-scoped
• Hoisting: Yes, but in temporal dead zone → cannot access before declaration
• Reassignable: Yes
• Redeclarable: No

function exampleLet() {
  if (true) {
    let y = 20;
    console.log(y); // 20
  }
  // console.log(y); // Error: y is not defined
}
exampleLet();

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3️⃣ const

• Scope: Block-scoped
• Hoisting: Yes, but in temporal dead zone
• Reassignable: No (cannot reassign the variable)
• Redeclarable: No
• Note: For objects/arrays, the reference is constant but properties/elements can change

const z = 30;
// z = 40; // Error: Assignment to constant variable

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

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Quick Comparison

Feature	var	let	const
Scope	Function	Block	Block
Hoisting	Yes (undefined)	Yes (TDZ)	Yes (TDZ)
Reassignable	Yes	Yes	No
Redeclarable	Yes	No	No
Use Case	Legacy code	Variables that change	Constants / fixed references

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⚡ In short:

Use let for variables that can change, const for constants, and avoid var in modern JS due to function scoping and hoisting issues.