Validation

By default, form data when submitted will be validated using HTML5 validation and the provided validator.

Tip

To disable HTML5 validation pass novalidate attribute to the form element.

Live validation (not recommended)

You can easily implement live validation by utilizing Svelte 5 reactivity

<script lang="ts">
  import { useForm2, SimpleForm, type Schema } from "@sjsf/form";
  import { translation } from "@sjsf/form/translations/en";
  import { theme } from "@sjsf/form/basic-theme";
  import { createValidator } from "@sjsf/ajv8-validator";

  const validator = createValidator();

  const schema: Schema = {
    type: "string",
    minLength: 10,
  };

  const form = useForm2({
    ...theme,
    initialValue: "initial",
    schema,
    validator,
    translation,
    onSubmit: console.log,
  });

  $effect(() => {
    form.errors = form.validate();
  });
</script>

<SimpleForm {form} style="display: flex; flex-direction: column; gap: 1rem" />

While it is possible, this approach has low efficiency because it is usually not meaningful to validate the entire form when only one field is changed.

Fields validation

Instead of performing a full form validation every time a field is changed, we propose to validate only the field being changed and full validation of the form on submission.

Note

By default, fields validation is performed with a debounce of 300ms.

This behavior can be changed using the fieldsValidationDebounceMs option.

<script lang="ts">
  import { ON_CHANGE, ON_INPUT, AFTER_SUBMITTED, SimpleForm } from "@sjsf/form";

  import { useCustomForm } from "@/components/custom-form";

  import { objectSchema } from "./_demo-schemas";

  const form = useCustomForm({
    schema: objectSchema,
    fieldsValidationMode: ON_INPUT | ON_CHANGE | AFTER_SUBMITTED,
    onSubmit: console.log,
  });
</script>

<SimpleForm
  {form}
  novalidate
  style="display: flex; flex-direction: column; gap: 1rem"
/>

The form in this example will validate fields during the input and change events only after the first submission of the form.

Fields validation mode API reference

Async validation

The form supports asynchronous validation.

Note

By default

• a new form validation process can only be started after the previous one is completed;
• a new fields validation process aborts the previous one.

You can change this behavior by passing the validationCombinator and fieldsValidationCombinator options.

To correctly display potential validation process errors, the handleValidationProcessError option should be used.

Note

By default, fields validation abort errors are not displayed

<script lang="ts">
  import Ajv, { type AsyncSchema, type SchemaValidateFunction } from "ajv";
  import { addFormComponents, createAsyncValidator } from "@sjsf/ajv8-validator";
  import { ON_INPUT, SimpleForm } from "@sjsf/form";
  import { handleValidationProcessError } from '@sjsf/form/translations/en';
  import { Status } from '@sjsf/form/use-mutation.svelte';

  import { useCustomForm } from "@/components/custom-form";

  const ajv = addFormComponents(new Ajv());
  const validate: SchemaValidateFunction = async (schema, data) => {
    await new Promise((resolve) => setTimeout(resolve, 1000));
    if (Math.random() > 0.5) {
      throw new Error("async error");
    }
    return data.length >= schema.minimum && data.length <= schema.maximum;
  };
  ajv.addKeyword({
    keyword: "asyncLength",
    async: true,
    type: "string",
    validate,
  });

  const schema: AsyncSchema = {
    $async: true,
    type: "string",
    pattern: "^\\d+$",
    asyncLength: {
      minimum: 3,
      maximum: 7,
    },
  };

  const form = useCustomForm({
    validator: createAsyncValidator({ ajv }),
    handleValidationProcessError,
    schema: schema,
    fieldsValidationMode: ON_INPUT,
    onSubmit: console.log,
  });

  const statusNames: Record<Status, string> = {
    [Status.IDLE]: "idle",
    [Status.Processed]: "processed",
    [Status.Success]: "success",
    [Status.Failed]: "failed",
  };
</script>

form validation: {statusNames[form.validation.status]}, fields validation: {statusNames[form.fieldsValidation.status]}
<SimpleForm
  {form}
  novalidate
  style="display: flex; flex-direction: column; gap: 1rem"
/>

Please see your validator page for more information.

Ajv

Zod

@cfworker/json-schema

Focus on first error

You can achieve focus on the first error by using the focusOnFirstError function.

<script lang="ts">
  import { SimpleForm } from "@sjsf/form";
  import { focusOnFirstError } from "@sjsf/form/focus-on-first-error";

  import { useCustomForm } from "@/components/custom-form";

  import { objectSchema } from "./_demo-schemas";

  const form = useCustomForm({
    schema: objectSchema,
    onSubmit: console.log,
    onSubmitError: focusOnFirstError,
  });
</script>

<SimpleForm
  {form}
  novalidate
  style="display: flex; flex-direction: column; gap: 1rem"
/>

1. focusOnFirstError will try to find a focusable element and focus it.
2. If it’s not found, it will try to find an errors list and scroll it into view.
3. If it’s not found, it will return false, so you can extend the behavior.

Errors list

If necessary, you can create a list of errors

<script lang="ts">
  import { SimpleForm } from "@sjsf/form";

  import { useCustomForm } from "@/components/custom-form";

  import { objectSchema } from "./_demo-schemas";

  const form = useCustomForm({
    schema: objectSchema,
    onSubmit: console.log,
  });
</script>

<SimpleForm
  {form}
  novalidate
  style="display: flex; flex-direction: column; gap: 1rem"
/>

{#if form.errors.size > 0}
  <div style="padding-top: 1rem;">
    <span style="font-size: larger; font-weight: bold;">Errors</span>
    <ui style="color: red;">
      {#each form.errors as [field, fieldErrors] (field)}
        {#each fieldErrors as err}
          <li>"{err.propertyTitle}" {err.message}</li>
        {/each}
      {/each}
    </ui>
  </div>
{/if}