Q41- What's the difference between let, const, and var in JavaScript?

In JavaScript, let, const, and var are used to declare variables — but they behave differently in terms of scope, reassignment, and hoisting.

---

1. var

• Scope: Function-scoped.
• Reassign: ✅ Yes.
• Redeclare: ✅ Yes.
• Hoisting: Variables declared with var are hoisted and initialized with undefined.

• Example:

  function test() {
    console.log(a); // undefined
    var a = 10;
    console.log(a); // 10
  }
  test();
  

---

2. let

• Scope: Block-scoped.
• Reassign: ✅ Yes.
• Redeclare: ❌ No (in the same scope).
• Hoisting: Hoisted but not initialized (Temporal Dead Zone).

• Example:

  {
    let x = 5;
    console.log(x); // 5
  }
  // console.log(x); // ❌ ReferenceError
  

---

3. const

• Scope: Block-scoped.
• Reassign: ❌ No (but object properties can be mutated).
• Redeclare: ❌ No.
• Hoisting: Hoisted but not initialized (Temporal Dead Zone).

• Example:

  const y = 10;
  // y = 20; // ❌ TypeError
  
  const obj = { name: 'Teekam' };
  obj.name = 'Singh'; // ✅ Allowed (mutating property)
  console.log(obj.name); // Singh
  

---

✅ When to use:

• var: ❌ Avoid in modern JS.
• let: When you need to reassign values.
• const: Default choice when value won’t change.