Summary  
This chapter explains how to declare and manage variables in JavaScript using `let` and `const`, illustrates reassignment rules, and advises using `const` by default.  

General domain of usage  
Web development


Variables are used to store data so it can be reused later in your code.

In JavaScript, variables are created using `let` or `const`.

```javascript
let age = 25;
const name = "John";
```

The difference between them is important.

A variable created with `let` can be reassigned:

```javascript
let count = 1;
count = 2;
```

A variable created with `const` cannot be reassigned:

```javascript id="z4m2qk"
const price = 100;
price = 200; // error
```

Use `const` by default, and use `let` only when you know the value will change.

Variables allow you to store values, update them, and use them in calculations or logic.


Learn the core concepts of JavaScript needed for backend development, including variables, data structures, functions, and asynchronous code. Practice working with real data and understand how JavaScript behaves outside the browser. Build a strong foundation before moving on to Node.js and server-side development.

Variables in JavaScript