27. What is scope in javascript?

In JavaScript, scope determines the accessibility (visibility) of variables, functions, and objects in different parts of the code. It defines where variables can be accessed and modified.

Types of Scope in JavaScript:

1. Global Scope

   • A variable declared outside of any function or block is in the global scope.
   • It can be accessed from anywhere in the code.

   js
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   let globalVar = "I am global";
   
   function showGlobal() {
       console.log(globalVar); // Accessible here
   }
   
   showGlobal();
   console.log(globalVar); // Accessible here too
   

2. Function Scope

   • Variables declared inside a function (var, let, or const) are only accessible within that function.

   js
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   function myFunction() {
       let funcVar = "I exist only inside this function";
       console.log(funcVar); // Accessible here
   }
   
   myFunction();
   console.log(funcVar); // ❌ Error: funcVar is not defined
   

3. Block Scope (ES6+)

   • Variables declared with let and const inside {} (blocks) are only accessible within that block.
   • var does not have block scope.

   js
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   {
       let blockVar = "I'm inside a block";
       console.log(blockVar); // ✅ Accessible here
   }
   
   console.log(blockVar); // ❌ Error: blockVar is not defined
   

4. Lexical Scope (Closure Scope)

   • Functions can access variables defined in their outer scope (parent function or global scope).

   js
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   function outer() {
       let outerVar = "I'm from the outer function";
   
       function inner() {
           console.log(outerVar); // ✅ Accessible due to lexical scope
       }
   
       inner();
   }
   
   outer();
   

5. Module Scope (ES6 Modules)

   • Variables declared inside a module are not accessible outside of it unless explicitly exported.

   js
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   // module.js
   const moduleVar = "I'm inside a module";
   export { moduleVar };
   
   // main.js
   import { moduleVar } from './module.js';
   console.log(moduleVar); // ✅ Accessible after import
   

Key Points:

• Global variables should be avoided as they can be modified from anywhere.
• Function scope means variables declared inside a function cannot be accessed outside.
• Block scope applies to let and const, preventing accidental modification.
• Lexical scope allows inner functions to access variables from their outer function.
• Modules help organize code and prevent pollution of the global scope.

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