Summary  
This chapter introduces how to declare and use variables for storing data in code, using `const` for values that shouldn’t change and `let` for values that can be updated and reused.

General domain of usage  
application state management


Variables are used to store data in your program.

Instead of repeating values everywhere, you save them in a variable and reuse them when needed.

In JavaScript, you will mostly use two keywords:

* `const`: for values that should not change;
* `let`: for values that can change.

Example:



const name = "Alex";
let count = 0;

count = count + 1;

console.log(name);
console.log(count);

Here, `name` stays the same, while `count` can be updated.

Using the right type of variable helps you write clearer and more predictable code.

Which keyword should you use for a value that will change?

Explore the core JavaScript concepts you need to start building apps. Learn how to store data, work with functions, handle arrays and objects, and write basic logic. The focus is on practical concepts used in React and React Native. 