React useState Hook

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

#React#React Hooks

4th August 2022

Time to read: 1 min

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Import useState

import React, {useState} from "react"

Initialize useState

useState accepts an initial state and returns two values:

  • The current state.
  • A function that updates the state.
function FavoriteColor() {
  const [color, setColor] = useState("");
}

In this case, the initial state to an empty string: useState("")

Read State

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

  return <h1>My favorite color is {color}!</h1>
}

Update State

To update state, use the state updater function.

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

  return (
    <>
      <h1>My favorite color is {color}!</h1>
      <button
        type="button"
        onClick={() => setColor("blue")}
      >Blue</button>
    </>
  )
}

What Can State Hold

The useState Hook can be used to keep track of strings, numbers, booleans, arrays, objects, or any combination of these:

function Car() {
  const [brand, setBrand] = useState("Ford");
  const [model, setModel] = useState("Mustang");
  const [year, setYear] = useState("1964");
  const [color, setColor] = useState("red");

  return (
    <>
      <h1>My {brand}</h1>
      <p>
        It is a {color} {model} from {year}.
      </p>
    </>
  )
}

Or, we can just use one state and include an object instead:

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

  return (
    <>
      <h1>My {car.brand}</h1>
      <p>
        It is a {car.color} {car.model} from {car.year}.
      </p>
    </>
  )
}

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.

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

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

  return (
    <>
      <h1>My {car.brand}</h1>
      <p>
        It is a {car.color} {car.model} from {car.year}.
      </p>
      <button
        type="button"
        onClick={updateColor}
      >Blue</button>
    </>
  )
}