react

Modal Dialogs in React

By Dave Ceddia

What’s the “react” way to trigger a modal when a button is clicked?

If you come from Angular, jQuery, or even just vanilla JS, your thought process for opening a modal dialog probably goes something like this:

  1. I need to open a modal.
  2. I’ll just call the modal function, which opens it up.
  3. Then the modal will wait for its “Close” button to be clicked.
  4. When “Close” is clicked I’ll call another function to close it.

But with React it’s like:

  1. I need to open a modal.
  2. What? How do I even

The root of the problem is this: How do you make something appear onscreen, in response to an event, in this new world where all you have is props and state? How can you make something happen?

A Modal

Let’s get right to it. I’ll just straight up give you a Modal component, and then we’ll walk through it:

import React from 'react';
import PropTypes from 'prop-types';

class Modal extends React.Component {
  render() {
    // Render nothing if the "show" prop is false
    if(!this.props.show) {
      return null;
    }

    // The gray background
    const backdropStyle = {
      position: 'fixed',
      top: 0,
      bottom: 0,
      left: 0,
      right: 0,
      backgroundColor: 'rgba(0,0,0,0.3)',
      padding: 50
    };

    // The modal "window"
    const modalStyle = {
      backgroundColor: '#fff',
      borderRadius: 5,
      maxWidth: 500,
      minHeight: 300,
      margin: '0 auto',
      padding: 30
    };

    return (
      <div className="backdrop" style={{backdropStyle}}>
        <div className="modal" style={{modalStyle}}>
          {this.props.children}

          <div className="footer">
            <button onClick={this.props.onClose}>
              Close
            </button>
          </div>
        </div>
      </div>
    );
  }
}

Modal.propTypes = {
  onClose: PropTypes.func.isRequired,
  show: PropTypes.bool,
  children: PropTypes.node
};

export default Modal;

This component is at least 50% inline styles by volume. I almost left them out, but I decided not to because having them really gives it the desired effect – the modal sits on top of a gray background that obscures everything behind it, and all you can do is click that Close button. If you try out this code you’ll see what I mean.

Modal in action

How It Works

The most important parts here are the first few lines, and the onClick handler.

This bit here is responsible for “showing” or “hiding” the modal:

if(!this.props.show) {
  return null;
}

Rather, it is either rendering the modal (when show is true) or nothing (when show is false).

Contrast this to jQuery where you might show and hide an element by toggling a CSS class, or maybe adding and removing it from the DOM.

The React way is different. There is no manual adding or removing of anything. Instead, it’s declarative. Pass show={true} to the Modal and it’s rendered. Pass show={false} and it isn’t.

So how, then, do you actually change that true/false value for show? How could you do it in response to a button click? It is actually up to the parent component – the “user” of Modal. Here is such a component:

import React, { Component } from 'react';
import Modal from './Modal';

class App extends Component {
  constructor(props) {
    super(props);

    this.state = { isOpen: false };
  }

  toggleModal = () => {
    this.setState({
      isOpen: !this.state.isOpen
    });
  }

  render() {
    return (
      <div className="App">
        <button onClick={this.toggleModal}>
          Open the modal
        </button>

        <Modal show={this.state.isOpen}
          onClose={this.toggleModal}>
          Here's some content for the modal
        </Modal>
      </div>
    );
  }
}

export default App;

When the App component first renders, its isOpen state is false, so the Modal is not rendered.

this.state = { isOpen: false };

Then when the user clicks the “Open the modal” button, it calls toggleModal which flips that flag to true.

toggleModal = () => {
  this.setState({
    isOpen: !this.state.isOpen
  });
}

The setState call triggers a re-render, and now Modal gets passed show={true}, so it appears.

Now what about closing it?

Notice we’re passing toggleModal as the onClose handler:

<Modal show={this.state.isOpen}
  onClose={this.toggleModal}>
  ...

Look back at the code for Modal and notice how the button calls the onClose prop when it’s clicked:

<button onClick={this.props.onClose}>
  Close
</button>

So that’s what’s happening: when the “Close” button is clicked, it calls the onClose prop – which is, in fact, the toggleModal function in App. That function flips the isOpen flag, which triggers a re-render, and the modal disappears. It’s truly gone, too: try a right-click “Inspect Element” while the modal is closed and you will notice the modal is nowhere to be found in the DOM.

This might be a bit mind-bending at first, but just do it a few times and it’ll become second nature.

Get the Code

Download a working example project on GitHub.

Learning React can be a struggle — so many libraries and tools!
My advice? Ignore all of them :)
For a step-by-step approach, check out my Pure React workshop.

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Dave Ceddia’s Pure React is a work of enormous clarity and depth. Hats off. I'm a React trainer in London and would thoroughly recommend this to all front end devs wanting to upskill or consolidate.

Alan Lavender
Alan Lavender
@lavenderlens