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 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.var or const in javascript
// var declares a variable, meaning its value will vary.
// const declares a constant, meaning its value will remain
// consistant and not change.
// If your variable changes throughout the program or website,
// declare it using a var statement.
// Otherwise, if its value does not change, declare it using
// a const statement.
const myConst='A const does not change.';
var myVar='A var does change.';
var myVar=2;Copyright © 2021 Codeinu
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