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.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.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.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
*/Copyright © 2021 Codeinu
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