JavaScript Scope

What is Scope?

Scope determines where variables can be accessed in your code. JavaScript uses lexical scoping - the position where variables are declared determines their accessibility.

Types of Scope

1. Global Scope

Variables declared outside any function or block:

var globalVar = "I'm global";
let globalLet = 'Also global';

function test() {
  console.log(globalVar); // Accessible everywhere
}

2. Function Scope

Variables declared inside a function:

function myFunction() {
  var functionScoped = 'Only inside function';
  console.log(functionScoped); // Works
}

// console.log(functionScoped); // Error: not defined

3. Block Scope

Variables declared inside {} blocks (let/const only):

if (true) {
  let blockScoped = 'Only in this block';
  var functionScoped = 'Available in entire function';
}

// console.log(blockScoped); // Error: not defined
console.log(functionScoped); // Works (var ignores block scope)

Scope Chain

JavaScript looks for variables from inner to outer scope:

var x = 'global';

function outer() {
  var x = 'outer';

  function inner() {
    var x = 'inner';
    console.log(x); // "inner" (finds closest scope)
  }

  inner();
  console.log(x); // "outer"
}

outer();
console.log(x); // "global"

Key Rules

• Inner scopes can access outer scope variables
• Outer scopes cannot access inner scope variables
• Variables are searched from innermost to outermost scope
• var is function-scoped, let/const are block-scoped