Modals come in handy when you want to notify the user of an important action that was performed successfully or not or when your quickly want to pass an information to your user as soon as they open your app. For example in an ecommerce app, when the user has hitted the complete order or checkout button, you may want to confirm the user's intention to proceed with the order by simply showing a modal requiring the user to either click the continue or cancel button. After completing the order, it is a common practice to also display a form of notification box to inform the user that the order was successfully placed.

There are other many use cases of modal, in fact there are cases that a login form in a modal is pop out for the user to login with.

In this tutorial, we will be making a modal with React useState and css.
The main purpose of this tutorial is to demonstrate to the reader how a modal can be made using the techniques stated above.
Understanding of the content of this article will enable the reader to be able to deploy the techniques in any way that suits his/her need.

In case you are starting from scratch, run any of the commands below to create react app or any equivalent command depending on your device and tool your are using.
Run the command in the folder you want to create the app.

yarn create react-app name_of_your_app

npx create-react-app name_of_your_app

In the src folder of the created app, I will a create folder called components. Then inside this folder I will make a
file and name it ModalPage.js. This file will contain two React components as follows

The first component is the Modal. This component will accept two props as defined below:

• isModalOpen: This is a react state that signifies if the modal is opened or not. It is of Boolean type that is, it is either true or false. When it is true, it implies the modal is opened while being false implies the modal is closed.

• closeModal: This is a function to close the modal. Hence this function will set the isModalOpen state value to false.
  

const Modal = ({isModalOpen, closeModal}) => {
  return (
    <div className={`${isModalOpen? 'modal open' : 'modal'}`}>
        <div className='modal-content'>
            <p>Modal opened click the close button below to close modal</p>
            <button className='btn close-modal' onClick={closeModal}>close modal</button>
        </div>
    </div>
  )
}

Note, that the className of the Modal component is conditionally set to be either modal or modal open depending on the value of isModalOpen using a ternary operator. When the value of isModalOpen is false the className of the Modal component will be modal while when its value is true the className of the Modal component will be modal open indicating the Modal is opened as explained above.
Also, there is a button inside the Modal which when clicked sets the the value of isModalOpen to false thereby closing the Modal. This is achieved by attaching an onClick event listener to button such that when it is clicked, the function closeModal is called and hence the value of the isModalOpen is set to false thereby closing the Modal.

The second component is the ModalPage described below.

In this component we define a state variable isModalOpen and corresponding function, setIsModalOpen to toggle its value using the React useState hook. isModalOpen is passed as prop to the Modal component.

Two functions are defined:

• closeModal: This function is used to set the value of isModalOpen to false, thereby closing the Modal. This function is passed as prop value to the Modal component.

• openModal: This function is used to set the value of isModalOpen to true thereby opening the Modal. The function is attached to a button in this component through onClick event. Hence, whenever the button is clicked, the value of isModalOpen is set to true and thereby opening the Modal
  

const ModalPage = () => {
    const [isModalOpen, setIsModalOpen] = useState(false)
    const closeModal = () => {
        setIsModalOpen(false)
    }
    const openModal = () => {
        setIsModalOpen(true)
    }
    return (
        <>
            <Modal closeModal={closeModal} isModalOpen={isModalOpen} />
            <main>
                <section className='page-element'>
                    <h1>Page content</h1>
                    <button className='btn open-modal' onClick={openModal}>open modal</button>
                </section>
            </main>
        </>
    )
}

export default ModalPage

Note: In case your Modal and ModalPage components are not in the same file, ensure you import the Modal component into the file containing the ModalPage component. Also, you can name your components whatever you like as long as they conform to React components naming convention.

Then write the following css inside your index.css located in the source folder of your react app.

.btn {
  cursor: pointer;
  border: none;
  padding: .5rem;
}

.modal {
  position: fixed;
  top: 0;
  left: 0;
  min-height: 100vh;
  width: 100vw;
  display: none;
}

.modal.open {
  display: grid;
  place-items: center;
  background-color: rgba(0, 0, 0, .5);
}
.modal-content {
  display: flex;
  flex-direction: column;
  width: 90%;
  max-width: 300px;
  padding: 1rem;
  background-color: #ffffff;
}

.close-modal {
  background-color: #d11a2a;
  color: #ffffff;
}

And in the App.js located in src folder of the created app, import the ModalPage component.

import ModalPage from './components/ModalPage';
function App() {
  return (
    <div>
      <ModalPage />
    </div>
  );
}

export default App;

Now, let's relate our css with our Modal component. Note the Modal can have its class to be either modal when the value of isModalOpen is false or modal open when the value of isModalOpen is true. This is where the logic lies. In the css file, element with class modal is given display property of none, that is not to display while element with class modal open is given display property of grid. Hence as the value of isModalOpen toggles between false and true, the Modal is removed and added back to the DOM appropriately.

Then render your App in the index.js located in the src folder of the created app

import React from 'react';
import ReactDOM from 'react-dom/client';
import './index.css';
import App from './App';
import reportWebVitals from './reportWebVitals';

const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>
);

Note, there are things you can change here, such as the styling of your modal content, where your declare the variables and function used and also the background color of the Modal. The most important information is understanding the technique used here.

Yes that is it with creating modal in ReactJS. Kindly put your questions or observations in the comment box below, I will be really grateful if I can use your insights to improve my work.

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