difference in var let and const
var:
* hoisted(global scope)
* function scope
let:
* block scope
* reassignable
* not redeclarable
const:
* block scope
* not reassignable
* not redeclarabledifference in var let and const
var:
* hoisted(global scope)
* function scope
let:
* block scope
* reassignable
* not redeclarable
const:
* block scope
* not reassignable
* not redeclarabledifference 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
*/difference between var, let, const
// var is a function scope ***
if(true){
var varVariable = 'This is var';
var varVariable = 'This is var again';
}
console.log(varVariable); // This is var again
// let is a block scope ***
if(true){
let letVariable = 'This is let';
let letVariable = 'This is let again';
// let variable can't re-define but we can re-assign value
console.log(letVariable); // let letVariable = 'This is let again';^SyntaxError: Identifier 'letVariable' has already been declared
}
console.log(letVariable); //ReferenceError: letVariable is not defined
// const variable can't re-define and re-assign value
// const is a block scope ***
if(true){
const constVarible = {
name: 'JavaScript',
age: '25 years',
};
constVarible.name = 'JS';
console.log(constVarible) // {name: 'JS',age: '25 years'} <= we can update const variable declared object
}Copyright © 2021 Codeinu
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