Scope in JavaScript

In JavaScript, Scope defines how variables are accessed and managed throughout the program. There are four types of scope:

• Global Scope
• Local Scope
• Block Scope
• Module Scope

Global Scope

Global scope is defined by variables that are declared outside of any function and can be accessed anywhere in the program.

var gVar = "Global Scope";
function globalScope(){
   console.log(gVar)
}
globalScope()
console.log(gVar)

Output

Local Scope

Local scope is defined by variables that are declared inside a function and can be accessed only within that function.

function localScope(){
   var lVar = "Local Scope";
   console.log(lVar)
}

localScope()
console.log(lVar)

Output

Block Scope

Before ES6, JavaScript had only two types of scope: global scope and local scope. After ES6, two new keywords, let and const, were introduced. These keywords provide block scope in JavaScript. A block is defined by { } and variables declared inside a block can only be accessed within that block.

function blockScope(){
   let blockVar = "Block Scope";
   console.log(blockVar);
}
blockScope()
console.log(blockVar);

Output

Module Scope

Module scope was officially introduced in JavaScript with ES6. In ES6, each module has its own scope, meaning variables and functions inside a module are private unless explicitly exported. This version introduced the import and export keywords, allowing modules to communicate with each other.

• Export: Allows you to share variables, functions, or classes from a module.
• Import: Allows you to bring in variables, functions, or classes from another module.

I hope this explanation clarifies the concept. If you have any questions or corrections, feel free to ask in the comments.

Comments

[Jon Randy 🎖️]

There are actually four types of scope. You missed Module scope.

[Ramya Sri M]

You're right, thank you for pointing that out! I'll make sure to update it.