This article covers creating a Riot Checkbox component, using the Material Design CSS BeerCSS. Before starting, make sure you have a base application running, or read my previous article Setup Riot + BeerCSS + Vite.

These articles form a series focusing on RiotJS paired with BeerCSS, designed to guide you through creating components and mastering best practices for building production-ready applications. I assume you have a foundational understanding of Riot; however, feel free to refer to the documentation if needed: https://riot.js.org/documentation/

Four checkbox states exist: unchecked, checked and disabled, and mixed (see the following screenshot). The goal is to create a checkbox Riot component with BeerCSS design and listen to click events.

Checkbox Component Base

First, create a new file named c-checkbox.riot under the components folder. The c- stands for "component", a useful naming convention and a good practice.

Into ./components/c-checkbox.riot, write the following HTML (found on the BeerCSS documentation):

<c-checkbox>
   <label class="checkbox" onclick={ inputClick } >
        <input type="checkbox" value={ props?.value ? true : false  } checked={ props?.value } disabled={ props?.disabled }>
        <span>{ props.label }</span>
    </label>
</c-checkbox>

Let's break down the code:

• The <c-checkbox> and </c-checkbox> defined a custom root tag, with the same name as the file. You must write it; otherwise, it may create unexpected results. Using the <label> as a root tag or redefining native HTML tags is a bad practice, so starting c- is a good naming.
• To enable the checked attribute, the props.value must exist and be true.
• The default value of a checkbox input is "on" as a String. It's not handy to manipulate in a Javascript application. Using the expression value={ props?.value ? true : false } make sure the checkbox value is always a Boolean, either true or false.
• On the Web Standards for a checkbox, the value and checked are two different attributes; the component unifies the input and checked values.
• Thanks to the props.disabled, the disabled attribute is conditionally assigned to the Input tag to disable the checkbox.
• If the label exists, it is injected into: <span>{props.label}</span>.

W3C states that a boolean property is true if the attribute is present — even if the value is empty or false. As mentioned in the documentation, Riot.js automatically fixes this behaviour: Boolean attributes (checked, selected, etc.) are ignored when the expression value is false:

<input type="checkbox" checked={ null }> becomes <input type="checkbox">
<input type="checkbox" checked={ '' }> becomes <input type="checkbox">
<input type="checkbox" checked={ false }> becomes <input type="checkbox">

In case the expression is true they will be correctly rendered according to the specs:

<input type="checkbox"  checked={ true }> becomes <input type="checkbox" checked='checked'>
<input type="checkbox"  checked={ 1 }> becomes <input type="checkbox"  checked='checked'>
<input type="checkbox"  checked={ 'is-valid' }> becomes <input type="checkbox"  checked='checked'>

Finally, the c-checkbox.riot can be instantiated into a front page index.riot:

<index-riot>
    <div style="width:600px;padding:20px;">
        <h4 style="margin-bottom:20px">Riot + BeerCSS</h4>
        <c-checkbox onclick={ clicked } value={ state.value } label={ state.value }/>
        <c-checkbox onclick={ clicked } label="Disabled" disabled={ true } />
        <c-checkbox onclick={ clicked } label="Disabled" disabled={ true } value="true" /> 
    </div>
    <script>
        import cCheckbox from "./components/c-checkbox.riot";

        export default {
            components: {
                cCheckbox
            },
            state: {
                value: true
            },
            clicked (ev) {
                if (ev.target.tagName === "SPAN") {
                    ev.stopPropagation()
                    ev.preventDefault();
                    this.update({ value: !this.state.value })
                }
            }
        }
    </script>
</index-riot>

Code break-down:

1. The component is imported with import cCheckbox from "./components/c-checkbox.riot"; then loaded into the components:{} Riot object.
2. On the HTML, the Button component is instantiated with <c-checkbox onclick={ clicked } />
3. The state of the checkbox is stored in state Riot object state: { value: false }. False is the default value.
4. The click event is watched: when the event click is fired, the function clicked is executed.
5. On click, the value is updated to its opposite with this.update({ value: !this.state.value })
6. An important issue occurs: the event click is emitted twice! The expression if (ev.target.tagName === "SPAN") is used to accept only one event, then the propagation of the even is stopped thanks to ev.stopPropagation(); and ev.preventDefault();.

Screenshot of the generated HTML:

Fix the checkbox issue: stop the double-click event

As mentioned in the previous section, the click event is fired twice. The issue is that clicking the label triggers a click on both the <c-checkbox> and the child checkbox input <input type="checkbox">.

The solution is to stop the event propagation inside the component, and re-emit the event once. During this moment, I take the opportunity to change the Boolean value to its opposite: the parent HTML will receive a change event with the correct value:

• If the input is checked, the change event emits true.
• If the input is unchecked, the change event emits false.

The c-checkbox.riot updated:

<c-checkbox >
    <label class="checkbox" onclick={ inputClick }>
        <input type="checkbox" value={ props?.value ? true : false  } checked={ props?.value } disabled={ props?.disabled }>
        <span>{ props.label }</span>
    </label>
    <script>
        export default {
            inputClick (e) {
                e.preventDefault();
                e.stopPropagation();
                this.root.value = this.props.value === true || this.props.value === "true" ? false : true;
                this.root.dispatchEvent(new Event('click'));
                this.root.dispatchEvent(new Event('change'));
            }
        }
    </script>
</c-checkbox>

Code breakdown:

• If a click occurs on the <label>, the click event is not propagated and cancelled, thanks to e.preventDefault(); and e.stopPropagation();
• The value of the checkbox input takes its opposite.
• The click and change events are re-emitted thanks to the dispatchEvent.

The value update on the parent component index.riot can be simplified:

<index-riot>
    <div style="width:600px;padding:20px;">
        <h4 style="margin-bottom:20px">Riot + BeerCSS</h4>
        <c-checkbox onclick={ clicked } value={ state.value } label={ state.value }/>
    </div>
    <script>
        import cCheckbox from "./components/c-checkbox.riot";

        export default {
            components: {
                cCheckbox
            },
            state: {
                value: false
            },
            clicked (ev) {
                this.update({ value: ev.target.value })
            }
        }
    </script>
</index-riot>

Now the state.value takes the value from the click Event, and the value always mirrors the current state of the checkbox.

Tips to simplify even more: It is not required to create a "clicked" function, one line is enough to update the value:

<c-checkbox onclick={ (ev) => update({ value: ev.target.value }) } value={ state.value } label={ state.value }/>

Checkbox Component Testing

It exists two methods for testing the Checkbox component, and it is covered in two different articles:

• Test with Vitest and Riot-SSR in a Node Environment
• Test with Vitest in a JsDom Environment

Conclusion

Voilà 🎉 We created a Checkbox Riot Component using Material Design elements with BeerCSS.

The source code of the checkbox is available on Github:
https://github.com/steevepay/riot-beercss/blob/main/components/c-checkbox.riot

Feel free to comment if you have questions or need help about RiotJS.

Have a great day! Cheers 🍻