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, 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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