Checkbox Groups
Learn how to build checkbox group inputs with Formsnap.
Checkbox groups are a set of checkboxes that allow users to select multiple options from a list, and are quite common in forms.
In this guide, you'll learn how to build a checkbox group with Formsnap by building an "Allergies" checkbox group, where a user must select any food allergies they have. We'll start with very basic functionality and then look at more advanced refinements for validation.
Create a Checkbox Group
For the purposes of this guide, we'll assume you're using the zod and zodClient adapters from Superforms, but the same principles apply to all adapters.
Define the Schema
Let's start by defining a schema that contains an array to hold the selected options. We'll create this inside the context="module" script tag of our Svelte component so we can access it in our component and +page.server.ts file.
<script lang="ts" context="module">
import { z } from "zod";
const allergies = ["None", "Peanuts", "Shellfish", "Lactose", "Gluten"] as const;
export const schema = z.object({
allergies: z
.array(z.enum(allergies))
.min(1, "If you don't have any allergies, select 'None'."),
});
</script>
We've defined an array named allergies that holds the possible enum values, and then created a schema that requires at least one option to be selected.
Setup the Load Function & Actions
Next, we'll create a +page.server.ts file where we'll define our load function and actions to handle the form submission.
import { superValidate } from "sveltekit-superforms";
import type { Actions, PageServerLoad } from "./$types";
import { schema } from "./+page.svelte";
import { zod } from "sveltekit-superforms/adapters";
import { fail } from "@sveltejs/kit";
export const load: PageServerLoad = async () => {
return {
form: await superValidate(zod(schema)),
};
};
export const actions: Actions = {
default: async (event) => {
const form = await superValidate(event, zod(schema));
if (!form.valid) {
return fail(400, { form });
}
return { form };
},
};
Notice we're importing that schema we defined in our +page.svelte file and using it to validate the form data in the load function and actions.
Initialize the SuperForm
Now that we have our schema defined and our load function and actions set up, we can initialize the SuperForm in our Svelte component.
<!-- script context="module" tag -->
<script lang="ts">
import { superForm } from "sveltekit-superforms";
import { zodClient } from "sveltekit-superforms/adapters";
import SuperDebug from "sveltekit-superforms";
let { data } = $props();
const form = superForm(data.form, {
validators: zodClient(schema),
});
const { form: formData } = form;
</script>
We're using the superForm function to initialize the form, passing in the form object from our load function and the zodClient adapter to handle client-side validation.
Import Components and Enhance the Form
Now that our SuperForm is initialized, we can use it to construct our checkbox group.
We'll first import the components we'll need from Formsnap, and then setup a form element with the enhance action to progressively enhance the form with client-side validation.
<!-- script context="module" tag -->
<script lang="ts">
import { superForm } from "sveltekit-superforms";
import { zodClient } from "sveltekit-superforms/adapters";
import { Fieldset, Legend, Label, Control, FieldErrors, Description } from "formsnap";
let { data } = $props();
const form = superForm(data.form, {
validators: zodClient(schema),
});
const { form: formData } = form;
</script>
<form method="POST" use:form.enhance>
<!-- ... -->
<button type="submit">Submit</button>
</form>
Construct the Fieldset
Since each checkbox in the group is related to a single field, we'll use a Fieldset component with a Legend to group them together. We'll use the Description component to provide more context about the fieldset and the FieldErrors component to display validation errors.
<!-- script tags -->
<form method="POST" use:form.enhance>
<Fieldset {form} name="allergies">
<Legend>Select your allergies</Legend>
<!-- ... -->
<Description>We'll accommodate your dietary restrictions.</Description>
<FieldErrors />
</Fieldset>
<button type="submit">Submit</button>
</form>
Next, we'll iterate over the allergies array and create a Control that includes a Label and a checkbox input for each option.
<!-- script tags -->
<form method="POST" use:form.enhance>
<Fieldset {form} name="allergies">
<Legend>Select your allergies</Legend>
{#each allergies as allergy}
<Control>
{#snippet children({ props })}
<input
type="checkbox"
{...props}
bind:group={$formData.allergies}
value={allergy}
/>
<Label>{value}</Label>
{/snippet}
</Control>
{/each}
<Description>We'll accommodate your dietary restrictions.</Description>
<FieldErrors />
</Fieldset>
<button type="submit">Submit</button>
</form>
Improve Validation
We now have a functional checkbox group that allows users to select multiple options from a list. However, we can make some improvements to enhance the user experience and provide better validation feedback.
You may have noticed that users can select "None" and another allergy at the same time, which doesn't make sense. We can address this by adding a refinement to our schema to ensure that if "None" is selected, no other allergies can be selected.
<script lang="ts" context="module">
import { z } from "zod";
const allergies = ["None", "Peanuts", "Shellfish", "Lactose", "Gluten"] as const;
export const schema = z.object({
allergies: z
.array(z.enum(allergies))
.min(1, "If you don't have any allergies, select 'None'.")
.refine((v) => {
return v.includes("None") ? v.length === 1 : true;
}, "If you select 'None', you can't select any other allergies."),
});
</script>
<!-- ...rest -->
We've added a refine method to the allergies array to ensure that if "None" is selected, no other allergies can be selected. If the user selects "None", the array length must be 1, otherwise the validation will fail and the custom error message will be displayed.
Finished Product
That's it! You've successfully created a checkbox group with Formsnap. With some custom styles and components applied, the finished product might look something like this:
TLDR - Show Me the Code
For those who prefer to skip the guide and get straight to the code, here's the code required to create a checkbox group with Formsnap.
import { superValidate } from "sveltekit-superforms";
import type { Actions, PageServerLoad } from "./$types";
import { schema } from "./+page.svelte";
import { zod } from "sveltekit-superforms/adapters";
import { fail } from "@sveltejs/kit";
export const load: PageServerLoad = async () => {
return {
form: await superValidate(zod(schema)),
};
};
export const actions: Actions = {
default: async (event) => {
const form = await superValidate(event, zod(schema));
if (!form.valid) {
return fail(400, { form });
}
return { form };
},
};
<script lang="ts" context="module">
import { z } from "zod";
export const allergies = ["None", "Peanuts", "Shellfish", "Lactose", "Gluten"] as const;
export const schema = z.object({
allergies: z
.array(z.enum(allergies))
.min(1, "If you don't have any allergies, select 'None'.")
.refine((v) => {
return v.includes("None") ? v.length === 1 : true;
}, "If you select 'None', you can't select any other allergies."),
});
</script>
<script lang="ts">
import { superForm } from "sveltekit-superforms";
import { zodClient } from "sveltekit-superforms/adapters";
import { Fieldset, Legend, Label, Control, FieldErrors, Description } from "formsnap";
let { data } = $props();
const form = superForm(data, {
validators: zodClient(schema),
});
const { form: formData } = form;
</script>
<form method="POST" use:form.enhance>
<Fieldset {form} name="allergies">
<Legend>Select any allergies you may have</Legend>
{#each allergies as allergy}
<Control>
{#snippet children({ props })}
<input
type="checkbox"
{...props}
bind:group={$formData.allergies}
value={allergy}
/>
<Label>{allergy}</Label>
{/snippet}
</Control>
{/each}
<Description>We'll accommodate your dietary restrictions.</Description>
<FieldErrors />
</Fieldset>
<button type="submit">Submit</button>
</form>