#164 What is var in JavaScript?

• var is a keyword in JavaScript used to declare variables.
• It was the only way to declare variables before ES6 (2015) introduced let and const.

---

🔹 Characteristics of var

1. Function Scoped

   • A var variable is only scoped to the function in which it is declared.
   • If declared outside any function, it becomes a global variable.

   function test() {
     if (true) {
       var x = 10;
     }
     console.log(x); // ✅ 10 (accessible because var is function-scoped)
   }
   test();
   

---

1. Hoisting

   • Variables declared with var are hoisted to the top of their scope.
   • However, they are initialized with undefined, not their value.

   console.log(a); // ✅ undefined (hoisted, but not assigned)
   var a = 5;
   

---

1. Can be re-declared and updated

   • You can declare the same variable multiple times with var.

   var a = 10;
   var a = 20; // ✅ allowed
   console.log(a); // 20
   

---

1. Global object property (in browsers → window)

   • If declared globally, a var variable becomes a property of the window object.

   var name = "Dev";
   console.log(window.name); // "Dev"
   

---

🔹 Problems with var (Why let and const were introduced)

❌ Function scope only → not block scoped, which can cause bugs.
❌ Hoisting confusion → can lead to undefined issues.
❌ Re-declaration allowed → can accidentally overwrite variables.

---

🔹 Example Comparison

if (true) {
  var a = 5;
  let b = 10;
  const c = 15;
}

console.log(a); // ✅ 5 (var is function-scoped, so accessible here)
console.log(b); // ❌ ReferenceError
console.log(c); // ❌ ReferenceError

---

🔹 Summary

✅ var → function-scoped, hoisted, re-declarable, added to global object.
✅ Introduced in ES1 (old JavaScript).
✅ Replaced by let and const in ES6 for better scoping and safety.