`var`, `let`, and `const` are probably the first words you hear about while learning JavaScript. Since the `let` keyword has been already explained in this [Answer](https://www.educative.io/answers/what-is-the-let-keyword-in-javascript), and `var` doesn't deserve a separate article yet, let's find out what `const` is:

# `const`
* `const` is a JavaScript keyword introduced by ES6 that doesn’t have a previous equivalent. 
```js
let x = 10;

const x = 10; //This is not possible.
```
* `const` creates block-scoped and read-only reference that cannot be reassigned. 


const x = 10;

x = 15;
console.log(x); //This is will throw an error because
//x is read-only

Read-only

const x = 10;

if(x == 10){
  const x = 15;
  console.log(x);
}

console.log(x);

Block-scope


* It is a good practice to write `const` identifiers in all-uppercase (to vary them from `let` variables).
```js
const TEMP_X = 10;
```
* A value assigned to the `const` keyword has to be initialized immediately. A `const` keyword without an assigned value will cause a syntax error.
```js
const X; //This is not possible.
```



What is the const keyword in JavaScript?

const is a JavaScript keyword from ES6 for block-scoped, read-only references that require immediate initialization.