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.difference between let, var and const in java script
//let is used to declare the variable or initialize a variable..
//let variable can be updated in future.
//Its block scope and we cannot redeclare it.
let a; // Initializing the variable.
let b = 4; // Initializing and declaring variable.
let b = 5; //Error:- cannot redeclare a value but we can update the value.
//var is just like let but var is used to declare a variable value at top of
//the program, its hoisted.
var a; // Initializing the variable.
var b = 4; // Initializing and declaring variable.
var b = 5; //b will be redeclared and we can update its value.
//const variable should be declared and intialized at same time.
//const variable cannot be updated in future.
//we cannot even redeclare the variable in future.
const a = 10; //Initilizing and declaring a variable at a time.
const b; //Error:- const should be declared and intialized.
const a = 11 // Error:- cannot redeclare the variable again.difference between var let and const in javascript with example
//functional scope
var a; // declaration
a=10; // initialization;
//global scope
// re-initialization possible
let a;//only blocked scope & re-initialization possible
a=10;
let a =20;
if(true){
let b =30;
}
console.log(b); // b is not defined
const // const also blocked scope,Re-initialization and re-declaration not possible
const a; // throws error {when we declaring the value we should assign the value.
const a =20;
if(true){
const b =30;
}
console.log(b); // b is not defined
console.log(a); // no output here because code execution break at leve b.Copyright © 2021 Codeinu
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