Answers for "difference between var and let and const in javascript"

19

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.
Posted by: Guest on May-11-2021
5

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.
Posted by: Guest on September-15-2021
5

what is the difference between let and const in javascript

The difference is that with const you can only only assign a value to a variable
once, but with let it allows you to reassign after it has been assigned.
Posted by: Guest on June-29-2020
0

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();
Posted by: Guest on July-26-2021
0

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.
Posted by: Guest on February-12-2021
0

difference between var and let and const in javascript

var variable1 // declared using var
const variable2 // declared using const

myFunction1();

function myFunction1() {
  variable1 = "hello!";
  console.log(variable1);
  // "hello!"
}

myFunction2();

function myFunction2() {
  variable2 = "hello!";
  // error: variable2 is a constant and can not be redifined
}

myFunction3(true);

myFunction3(codition) {
  if(condition) {
    let variable3 = "helo!" // declared using const
  }
  variable3 = "hello!";
  // error: variable3 is out of scope
}

/*

Therefore, 
  
  var:
    -can be declared outside any function to be used inside any function
    -can be declared inside any function or any other {} which are of only if or if-else or switch etc. and can be used anywhere inside the function
    -can be changed again and again anywhere
  let:
    -can be declared outside any function to be used inside any function
    -if declared inside any function or any other {} which are of only if or if-else or switch etc. and can't be used anywhere inside the function and can be only used inside statement
    - can be changed again and again only inside the statement in which they are made in
    const:
    -can be declared outside any function to be used inside any function
    -can be declared inside any function or any other {} which are of only if or if-else or switch etc. and can be used anywhere inside the function
    -cannot be changed again and agan anywhere, if tried to, will result in an error

*/
Posted by: Guest on July-23-2021

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