var vs let vs const
var:
- hoisted (always declared at top of scope, global if none)
- function scope
let:
- block scope
- not redeclarable
const:
- block scope
- not reassignable
- not redeclarable
Note: Although it may seem like these hold only semantic meaning, using the
appropriate keywords helps the JS engines' compiler to decide on what to optimize.let vs var vs const
// ⚡ Initialization
var a; //✅
let b; //✅
const c; //❌ const must have an initial value
// ⚡ Re-Assignment
var d = 1;
d = 10; //✅
let e = 2;
e = 20; //✅
const f = 3;
f = 30 //❌ const value is always constant and cannot be reassigned
// ⚡ Re-Declaration
var g = 1;
var g = 10; //✅
let h = 2;
let h = 20; //❌ must use variable name only to reassign, cannot be reassigned
const i = 3;
const i = 30 //❌ cannot be reassigned
// ⚡ Scope [Global, Function or local and block scope]
// Global Scope ==> Any variable that is declared outside any of the function
// Function Scope(var) ==> Can be accessed inside the function it was declared and its child
// Block Scope(let and const) ==> Con be accessed inside curly brackets where it was declared and its child
function myFunction(){
var myName1 = 'Asmita';
let myName2 = 'Dikshit';
const myName3 = 'Sizen';
console.log(myName1);
console.log(myName2);
console.log(myName3);
if(true){
console.log(myName1);
console.log(myName2);
console.log(myName3);
var myAge1 = 13;
let myAge2 = 15;
const myAge3 = 14;
console.log(myAge1);
console.log(myAge2);
console.log(myAge3);
}
console.log(myName1);
console.log(myName2);
console.log(myName3);
console.log(myAge1);
console.log(myAge2);
console.log(myAge3);
};
myFunction();Copyright © 2021 Codeinu
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