# JavaScript var, let and const

### 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.

```javascript
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.
```

1. **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.

```javascript
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
```

1. **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.

```javascript
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.