How to add a Dark Mode Toggle in React

When I rebuilt my portfolio site, I knew I wanted to have some fun with the design, and a dark and light mode fit the bill. I enjoyed a lot of the discoveries I made during this project, but my favorite has to be the color-changing SVGs. This tutorial assumes familiarity with React, and I am using v17.0.1 and functional components.

First, I created a base layout. Next, I put together my dark and light color schemes. It took a little trial and error, but after testing all my combinations for sufficient contrast and experimenting with placement, I found I needed 6 CSS variables. I guess you could say I used “dark first” development because the variable names make sense in the context of the dark theme. The light theme has less variation but needed --button-border where --accent would be the same color as the background.

.theme-dark {
  --dark-text: #292929;
  --light-text: #F9F8F8;  
  --dark-background: #2F4550;
  --light-background: #586F7C;
  --accent: #B8DBD9;
  --button-border: #B8DBD9;
}

.theme-light {
  --dark-text: #5E4B56;
  --light-text: #5E4B56;
  --dark-background: #DBE7E4;
  --light-background: #EDDCD2;
  --accent: #DBE7E4;
  --button-border: #5E4B56;
}

Then, I set about applying colors to my base layout:

html, #root {
  background-color: var(--dark-background);
  color: var(--dark-text);
}

nav {
  background-color: var(--dark-background);
  color: var(--light-text);
}

.main-container {
  background-color: var(--light-background);
}

I also set the backgrounds of the sections of content that I wanted to pop to --accent. --dark-text would have worked on all backgrounds in the dark theme, but I set the section titles to --light-text to make them stand out more.

I found Musthaq Ahamad‘s basic theme switcher tutorial, and set about applying it to functional React components.I put functions for changing the theme and checking localStorage for theme preferences into a file called themes.js.

function setTheme(themeName) {
    localStorage.setItem('theme', themeName);
    document.documentElement.className = themeName;
}

function keepTheme() {
  if (localStorage.getItem('theme')) {
    if (localStorage.getItem('theme') === 'theme-dark') {
      setTheme('theme-dark');
    } else if (localStorage.getItem('theme') === 'theme-light') {
      setTheme('theme-light')
    }
  } else {
    setTheme('theme-dark')
  }
}

module.exports = {
  setTheme,
  keepTheme
}

In my App.js file, I added keepTheme() to my useEffect().

import { keepTheme } from './utils/themes';

function App() {
  useEffect(() => {
      keepTheme();
  })
}

Next, I added the toggle component to my navigation bar component. I styled the toggle following Chris Bongers’ Tutorial based on Katia De Juan’s Dribbble. Then I adjusted the size and flipped it to default to dark mode. While this toggle is so cute that you could die, this tutorial will work with any <button> or clickable <input>. First, I set up the basic JSX, the local state, and a variable to hold the theme we get from localStorage:

import React, { useEffect, useState } from 'react';
import '../styles/toggle.css';
import { setTheme } from '../utils/themes';

function Toggle() {
  const [togClass, setTogClass] = useState('dark');
  let theme = localStorage.getItem('theme');
  return (
        <div className="container--toggle">
           <input type="checkbox" id="toggle" className="toggle--checkbox" onClick={handleOnClick} />
            <label htmlFor="toggle" className="toggle--label">
                <span className="toggle--label-background"></span>
            </label>
        </div>
    )
}

export default Toggle;

When a user clicks the toggle, I want the theme on the page to change and the toggle to change with it. I added the imported setTheme() function and setTogClass() from the local state to a handleOnClick function. You can see where it is passed to the clickable part of the toggle in the JSX above.

const handleOnClick = () => {
  if (localStorage.getItem('theme') === 'theme-dark') {
      setTheme('theme-light');
      setTogClass('light')
  } else {
      setTheme('theme-dark');
      setTogClass('dark')
  }
}

I used this component’s useEffect() to make sure the local state togClass always loads with the correct theme.

useEffect(() => {
    if (localStorage.getItem('theme') === 'theme-dark') {
        setTogClass('dark')
    } else if (localStorage.getItem('theme') === 'theme-light') {
        setTogClass('light')
    }
}, [theme])

Because my toggle is a checkbox, the dark theme should show the unchecked (moon) state and the light theme should show the checked (sun) state. I couldn’t get defaultChecked to work how I wanted, so I replaced the unchecked <input> with this conditional rendering ternary operator (conditional operator):

{
    togClass === "light" ?
    <input type="checkbox" id="toggle" className="toggle--checkbox" onClick={handleOnClick} checked />
    :
    <input type="checkbox" id="toggle" className="toggle--checkbox" onClick={handleOnClick} />
}

If you used a <button>, you could easily use conditional rendering like this to change the className attribute within the <button> tag and get the same effect.

Put all together, the code for the toggle component looks like this:

import React, { useEffect, useState } from 'react';
import '../styles/toggle.css';
import { setTheme } from '../utils/themes';

function Toggle() {
    const [togClass, setTogClass] = useState('dark');
    let theme = localStorage.getItem('theme');

    const handleOnClick = () => {
        if (localStorage.getItem('theme') === 'theme-dark') {
            setTheme('theme-light');
            setTogClass('light')
        } else {
            setTheme('theme-dark');
            setTogClass('dark')
        }
    }

    useEffect(() => {
        if (localStorage.getItem('theme') === 'theme-dark') {
            setTogClass('dark')
        } else if (localStorage.getItem('theme') === 'theme-light') {
            setTogClass('light')
        }
    }, [theme])

    return (
        <div className="container--toggle">
            {
                togClass === "light" ?
                <input type="checkbox" id="toggle" className="toggle--checkbox" onClick={handleOnClick} checked />
                :
                <input type="checkbox" id="toggle" className="toggle--checkbox" onClick={handleOnClick} />
            }
            <label htmlFor="toggle" className="toggle--label">
                <span className="toggle--label-background"></span>
            </label>
        </div>
    )
}

Update

To see how I have refactored the logic of this component and made it accessible, read An Accessible Dark Mode Toggle in React.

Finally, my favorite part: the color switching SVGs! CSS variables work in SVG code too!

I got my SVG code for the Github and Chrome icons from DEVICON. For the Github icon all I had to change was one fill attribute in a <g>:

<g fill="var(--dark-text)">

The Chrome icon had a fill attribute in a <circle> and a <path>:

<circle fill="var(--dark-text)" cx="63.624" cy="64.474" r="22.634"></circle><path fill="var(--dark-text)" ...>

The result looks like this:

Conclusion

I tried to include all of the relevant code, but you can also see the full code for my site in its Github repository. If you enjoyed this article or are left with questions, please leave a comment! I would also love to see anything built following this tutorial.

Also Published here