JavaScript - var Keyword

Overview

Estimated time: 10–15 minutes

var is function-scoped and hoisted. Prefer let/const to avoid surprises.

Learning Objectives

• Understand function scope vs block scope.
• Recognize hoisting and redeclaration hazards.

Prerequisites

• JavaScript - Constants (const)

Function scope

function demo(){
  if (true) {
    var x = 1;
  }
  console.log(x); // 1 (function scoped)
}

Hoisting and redeclaration

console.log(a); // undefined (hoisted declaration)
var a = 10;
var a = 20;      // redeclaration allowed

Recommendation

• Use const by default; let when reassignment is needed; avoid var.