Posted on Aug 17, 2021

Var vs Let vs Const in JavaScript

Let's understand comparison between var, let and const.

Variables defined with var declarations are globally scoped or function scoped and let and const has block scope or we can say local scope.

example:

var testVar = 'var'; // global scope let testLet = 'let'; // local scope const testConst= 'const'; // local scope function testScope { consol.log(window.testVar); // var consol.log(window.testLet); // undefined consol.log(window.testConst); // undefined } testScope() // output var

Variables defined with var can be Redeclared but with let and const cannot be Redeclared.

example :

var testVar = 10; let testLet = 10; const testConst = 10; function test{ var testVar = 20; // it will work let testLet = 20; // it will throw error const testConst = 20; // it will throw error console.log(testVar,testLet,testConst); } test();

Var can updated and re-declared.

Let can be updated but not re-declared.

Const cannot be updated and re-declared.

example :

var testVar = 10; let testLet = 10; const testConst = 10; function test{ testVar = 20; // it will work testLet = 20; // it will work testConst = 20; // it will throw error console.log(testVar,testLet,testConst); } test();