Scope

Scope in JavaScript refers to the context in which variables and functions are accessible. It determines the visibility and lifetime of these variables and functions.

Types of Scope

• Global Scope: Variables declared outside any function are in the global scope and can be accessed from anywhere in the code.
• Function Scope: Variables declared within a function are in the function scope and can only be accessed within that function.
• Block Scope: Variables declared with let or const within a block (e.g., inside curly braces {}) are in the block scope and can only be accessed within that block.

Global Scope

Variables declared outside any function have global scope:

let globalVar = "I am global";

function showGlobalVar() {
    console.log(globalVar); // Accessible here
}

showGlobalVar();
console.log(globalVar); // Accessible here too

Function Scope

Variables declared within a function have function scope:

function myFunction() {
    let functionVar = "I am local to this function";
    console.log(functionVar); // Accessible here
}

myFunction();
console.log(functionVar); // Error: functionVar is not defined

Block Scope

Variables declared with let or const within a block have block scope:

{
    let blockVar = "I am block scoped";
    console.log(blockVar); // Accessible here
}

console.log(blockVar); // Error: blockVar is not defined

Scope Chain

JavaScript uses a scope chain to resolve variable references. If a variable is not found in the current scope, JavaScript looks up the scope chain to find it.

let outerVar = "I am outside";

function outerFunction() {
    let innerVar = "I am inside";
    
    function innerFunction() {
        console.log(outerVar); // Accessible here
        console.log(innerVar); // Accessible here
    }
    
    innerFunction();
}

outerFunction();

For more detailed information, you can check out resources like W3Schools and MDN Web Docs.