Table of contents-
Introduction
var
let
const
Introduction
Everyone knows JavaScript as one of the most popular web design languages, which makes our web page attractive and dynamic.
Let's see about Javascript variable declaration keywords-
1. var
var is the oldest keyword used in javascript but now in modern Javascript mostly we try to avoid it, why? Behind it is a reason-
When we use var for any variable it makes that variable globally accessible, you may take it as a feature of var or disadvantage too..What happens when someone changes the value of the var variable? For this reason, we try to avoid it.
var x = 1;
if (x === 1) {
var x = 2;
console.log(x);
}
console.log(x);
// output will be the 2,2 because we redecalred it.
- let
This keyword comes to avoid the disadvantage of var, it provides block-level access.
The scope of a let variable is only block-scoped. It can’t be accessible outside the particular block ({block}) means no other part of the code can change it.
let a = 10
if (true) {
let a = 9
console.log(a) // It prints 9 & cant use outside the block
}
console.log(a) // It prints 10
- const
This is also a block-level keyword, but a restriction you must have to initialize it to use.
And also after the initialization you cant update it anywhere else. const keyword has its specific use.
const a = {
value1: 1,
value2: 9
}
// It is allowed
a.value3 = 3
// It is not allowed
a = {
b: 10,
value2: 9
}
Hope this article may be helpful to everyone.