<theme-toggle>

A custom element that allows you to toggle between light, dark and system theme.

How it works

By default, the component determines the theme from user's system preferences using the prefers-color-scheme media query. When the theme is changed, by clicking the toggle button, the selected theme is saved in localStorage if noStorage is false (default). A data-theme attibute is added to the root element of the document, with the appropriate value (light, dark, system). The default value is system, but if the user has previously selected a theme and the noStorage property is not set to true, the saved theme is used instead.

API documentation • Demo

Install

$ npm install --save @georapbox/theme-toggle-element

Usage

Script

import { ThemeToggle } from './node_modules/@georapbox/theme-toggle-element/dist/theme-toggle.js';

// Manually define the element.
ThemeToggle.defineCustomElement();

Alternatively, you can import the automatically defined custom element.

import './node_modules/@georapbox/theme-toggle-element/dist/theme-toggle-defined.js';

Markup

<theme-toggle storage-key="theme-preference"></theme-toggle>

Style

The component comes with a bare minimum style, but you can override it by using the CSS Parts provided. See the usage example for more details.

API

Properties

Name	Reflects	Type	Required	Description
noStorage no-storage	✓	Boolean	-	Indicates whether the theme state should be persisted to local storage. Any previously saved preference is ignored, but is not removed from local storage.
storageKey storage-key	✓	String	-	The key to be used in local storage to save the theme preference. If omitted, the default value is theme-toggle/theme-preference. If noStorage is true, this property is ignored.
noIcon no-icon	✓	Boolean	-	Indicates whether the icon should be displayed or not.
noLabel no-label	✓	Boolean	-	Indicates whether the label should be displayed or not. For accessibility reasons, the label is only visually hidden, but still available to screen readers.

Slots

Name	Description
light	The content for the light theme (icon and label).
icon-light	The content for the light theme icon.
label-light	The content for the light theme label.
dark	The content for the dark theme (icon and label).
icon-dark	The content for the dark theme icon.
label-dark	The content for the dark theme label.
system	The content for the system theme (icon and label).
icon-system	The content for the system theme icon.
label-system	The content for the system theme label.

CSS Parts

Name	Description
base	The componen'ts base wrapper. In this case this is a native <button> element.
icon	The icon's wrapper element (including the light, dark and system theme icons).
icon-light	The light theme icon's wrapper element.
icon-dark	The dark theme icon's wrapper element.
icon-system	The system theme icon's wrapper element.
label	The label's wrapper element (including the light, dark and system theme labels).
label-light	The light theme label's wrapper element.
label-dark	The dark theme label's wrapper element.
label-system	The system theme label's wrapper element.

Methods

Name	Type	Description	Arguments
defineCustomElement	Static	Defines/registers the custom element with the name provided. If no name is provided, the default name is used. The method checks if the element is already defined, hence will skip trying to redefine it.	elementName='theme-toggle'

Events

Name	Description	Event Detail
tt-theme-change	Emitted when theme changes by user's interaction.	{theme: 'light' | 'dark' | 'system'}

Usage example

HTML

<theme-toggle></theme-toggle>

CSS

Customize the component's appearance by using CSS custom properties and CSS parts.

:root {
  --body-color: #000;
  --body-bg-color: #fff;
}

@media (prefers-color-scheme: dark) {
  :root {
    --body-color: #fff;
    --body-bg-color: #000;
  }
}

:root[data-theme="light"] {
  --body-color: #000;
  --body-bg-color: #fff;
}

:root[data-theme="dark"] {
  --body-color: #fff;
  --body-bg-color: #000;
}

theme-toggle:not(:defined) {
  display: none;
}

theme-toggle::part(base) {
  border: 1px solid var(--body-color);
}

JavaScript

import { ThemeToggle } from './node_modules/@georapbox/theme-toggle-element/dist/theme-toggle.js';

ThemeToggle.defineCustomElement();

documemt.addEventListener('tt-theme-change', evt => {
  console.log('tt-theme-change ->', evt.detail);
});

Changelog

For API updates and breaking changes, check the CHANGELOG.

Development setup

Prerequisites

The project requires Node.js and npm to be installed on your environment. Preferrably, use nvm Node Version Manager and use the version of Node.js specified in the .nvmrc file by running nvm use.

Install dependencies

Install the project dependencies by running the following command.

npm install

Build for development

Watch for changes and start a development server by running the following command.

npm start

Linting

Lint the code by running the following command.

npm run lint

Testing

Run the tests by running any of the following commands.

npm test
npm run test:watch # watch mode

Build for production

Create a production build by running the following command.

npm run build

License

The MIT License (MIT)