React useState Hook allows us to track state in a function component.

State generally refers to data or properties that need to be tracking in an application.

Import useState
To use the useState Hook, we first need to import it into our component.

Example:Get your own React.js Server
At the top of your component, import the useState Hook.

import { useState } from "react";
Notice that we are destructuring useState from react as it is a named export.

To learn more about destructuring, check out the ES6 section.

Initialize useState
We initialize our state by calling useState in our function component.

useState accepts an initial state and returns two values:

The current state.
A function that updates the state.
Example:
Initialize state at the top of the function component.

import { useState } from "react";

function FavoriteColor() {
const [color, setColor] = useState("");
}
Notice that again, we are destructuring the returned values from useState.

The first value, color, is our current state.

The second value, setColor, is the function that is used to update our state.

These names are variables that can be named anything you would like.

Lastly, we set the initial state to an empty string: useState("")

Read State
We can now include our state anywhere in our component.

Example:
Use the state variable in the rendered component.

import { useState } from "react";
import ReactDOM from "react-dom/client";

function FavoriteColor() {
const [color, setColor] = useState("red");

return

My favorite color is {color}!

}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(<FavoriteColor

Update State
To update our state, we use our state updater function.

We should never directly update state. Ex: color = "red" is not allowed.

Example:
Use a button to update the state:

import { useState } from "react";
import ReactDOM from "react-dom/client";

function FavoriteColor() {
const [color, setColor] = useState("red");

return (
<>

My favorite color is {color}!

type="button"
onClick={() => setColor("blue")}
>Blue
</>
)
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render();

Update State
To update our state, we use our state updater function.

We should never directly update state. Ex: color = "red" is not allowed.

Example:
Use a button to update the state:

import { useState } from "react";
import ReactDOM from "react-dom/client";

function FavoriteColor() {
const [color, setColor] = useState("red");

return (
<>

My favorite color is {color}!

type="button"
onClick={() => setColor("blue")}
>Blue
</>
)
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render();

Updating Objects and Arrays in State
When state is updated, the entire state gets overwritten.

What if we only want to update the color of our car?

If we only called setCar({color: "blue"}), this would remove the brand, model, and year from our state.

We can use the JavaScript spread operator to help us.

Example:
Use the JavaScript spread operator to update only the color of the car:

import { useState } from "react";
import ReactDOM from "react-dom/client";

function Car() {
const [car, setCar] = useState({
brand: "Ford",
model: "Mustang",
year: "1964",
color: "red"
});

const updateColor = () => {
setCar(previousState => {
return { ...previousState, color: "blue" }
});
}

return (
<>

My {car.brand}

It is a {car.color} {car.model} from {car.year}.

type="button"
onClick={updateColor}
>Blue
</>
)
}

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render();