Skip to content

Advanced JavaScript form validation

Hyvä mostly uses built-in browser form validation. For many use cases that's enough, but in some cases JavaScript validation is required (for example, to display custom validation messages in a specific location).

The JS form validation library is available since Hyvä 1.1.14

Getting started

1. Enable advanced JS validation

Load the advanced form validation on the pages your want to use it using layout XML by applying the layout handle hyva_form_validation.

<page xmlns:xsi=""
    <update handle="hyva_form_validation"/>

2. Initialize the form validation Alpine.js component

If you only need the form validation on frontend logic, use x-data="hyva.formValidation($el)" to initialize the component.

<form x-data="hyva.formValidation($el)">

If additional logic is needed, merge the form validation component with your custom component properties:

<form x-data="{...initMyCustomComponent(), ...hyva.formValidation($el)}">

You can trigger the validation of the whole form using the Alpine.js @submit event with the onSubmit method.

<form x-data="hyva.formValidation($el)" @submit="onSubmit">

Validation of individual fields can be triggered using the @change event with the onChange method.

<div class="field field-reserved">
    <input name="example" data-validate='{"required": true}' @change="onChange" />

Form Submit Action

The default submit action is prevented to stop the form from submitting until all fields are correct.
For this purpose the novalidate attribute is added to the FORM element automatically.

The field field-reserved classes on the wrapper element are used to reserve some space below the input element so no layout shift occurs when an error message is displayed.

3. Define the validation rules

Validation rules can be added using data-validate or using HTML5 browser constraints API.

To add a custom validator, use this syntax:

<div class="field field-reserved">
    <input type="number" data-validate='{"min": 2, "required": true}' />


Use regular JSON object notation (not plain JavaScript), because the content of the data-validate attribute is parsed with JSON.parse().

You can also use some browser HTML5 constraint attributes (see below for a list of supported native validation rules):

<div class="field field-reserved">
    <input type="number" min="2" required />

Wrapper classes

Input elements should be wrapped by a container element with the CSS classes field field-reserved.
It is also possible to use custom class names instead of class="field field-reserved" (check out the Advanced settings section below).

If there is no container element with those classes, it will be generated automatically at the time an error messages is shown.

Available validators

Name Usage examples Note
required required
data-validate='{"required": true}'
Uses the browser constraint API validation
minlength minlength="2"
data-validate='{"minlength": 2}'
Uses the browser constraint API on text input
maxlength maxlength="3"
data-validate='{"maxlength": 3}'
Uses the browser constraint API on text input
min min="2"
data-validate='{"min": 2}'
Uses the browser constraint API on number inputs
max max="4"
data-validate='{"max": 3}'
Uses the browser constraint API on number inputs
step step="1"
data-validate='{"step": 1}'
Uses the browser constraint API on number inputs
email type="email"
data-validate='{"email": true}'
Uses the Magento email validation regex
password type="password"
data-validate='{"password": true}'
Uses the Magento password validation regex
equalTo data-validate='{"equalTo": "password"}' Compares a field value with other field value

Custom validators can be added using the method hyva.formValidation.addRule (see below).

Examples of usage in templates

<div class="field field-reserved">
    <input name="first-name" data-validate='{"required": true}' />

<div class="field field-reserved">
    <input name="last-name" data-validate='{"maxlength": 20}' required />

<div class="field field-reserved">
    <input name="last-name" 
           data-validate='{"maxlength": 20}' 
           data-msg-maxlength='<?= /* @noEscape  */  __("Max length of this field is "%0"") ?>'

<div class="field field-reserved">
    <input name="city" minlength="3" required />

<!-- Grouping several fields in one container -->
<div class="field field-reserved grid grid-cols-2">
        <label for="name"><?= $escaper->escapeHtml(__('Your Name')) ?></label>
        <input id="name" name="name" type="text" required @blur="onChange"/>
        <label for="hotel"><?= $escaper->escapeHtml(__('Hotel Name')) ?></label>
        <input id="hotel" name="hotel" type="text"
               data-validate='{ "required": true, "minlength": 5 }'
               data-msg-required="<?= $escaper->escapeHtmlAttr('Enter a valid hotel name.') ?>"/>

The data-msg-VALIDATOR_NAME attribute allows overriding the default validator message.
The %0 placeholder will be replaced with the validation rule argument.

Validating a single field during user interaction

Use the onChange callback with the input event to trigger field validation during user interaction.

<input @input="onChange" data-validate="..."/>

Custom submit function

Custom form submission can be accomplished with hyva.formValidation:

<form x-data="{...hyva.formValidation($el), ...initMyForm()}" 
function initMyForm() {
    return {
        myFormSubmit(event) {

                .then(() => {
                    // all fields validated
                .catch((invalid) => {
                    if (invalid.length > 0) {

Adding new validation rules

To add new validation rule, use the hyva.formValidation.addRule method and pass new validation function.
The first argument is the validator name and the second argument is the validator rule callback.

A validator rule callback is a function that will receive four arguments:

 * Validator arguments
 * @param {string} value - input value
 * @param {*} options - additional options passed by data-validator='{"validatorName": {"option": 1}}'
 * @param {Object} field - Alpine.js object which contains element, validators and validation state // TODO MAKE CLEARER
 * @param {Object} context - The Alpine.js component instance
hyva.formValidation.addRule('phone', function(value, options, field, context) {
    const phoneNumber = value.trim().replace(' ', '');
    if (phoneNumber.length !== 9) {
        // return message if validation fails;
        return '<?= $escaper->escapeJs(__("Enter correct phone number, like XXX XXX XXX")) ?>';
    } else {
        // return true if validation passed
        return true;

Validation rule functions should return one of the following values:

  • The boolean true if the rule is valid.
  • A string message if the rule is invalid. The string should describe the failure in a helpful way
  • A Promise that resolves to true or a message string when the validation completes.
    See below for more information on asynchronous validation rules.

Asynchronous validation

Sometimes validation of form values requires asynchronous actions, such as sending a query to a web API and waiting for the response.

This can be accomplished by returning a promise from the validation function.

The form submission is prevented by the onSubmit function until either all validation rules pass or the one of the fields has an invalid value. For fields with async validators, error messages will be displayed as soon as all field rules have completed.

Example async validator rule

hyva.formValidation.addRule('username', (value, options, field, context) => {
    return new Promise(resolve => {
        // show the user form validation is ongoing, maybe show a spinner
        field.element.disabled = true;

        fetch(this.url + '?form_key=' + hyva.getFormKey(), {
            method: 'post',
            body: JSON.stringify({username: value}),
            headers: {contentType: 'application/json'}
            .then(response => response.json())
            .then(result => {
                if (result.ok) {
                } else {
                    resolve(hyva.strf('The username "%0" is already taken.', value));
            .finally(() => {
                // indicate validation has finished, remove spinner if shown
                field.element.disabled = false;

Advanced settings

Initialization options

To customize the class names used by validator rules, passing an object with options as a second argument to hyva.formValidation.

<form x-data="hyva.formValidation($el, {fieldWrapperClassName: 'fld', messagesWrapperClassName: 'msg'})"></form>

Default values:

    "fieldWrapperClassName": "field field-reserved",
    "messagesWrapperClassName": "messages",
    "validClassName": "field-success",
    "invalidClassName": "field-error"

Validation rules with a dependency on another field

Sometimes field validation is dependent on another field. For example purposes, let's create conditional validation for ZIP codes:

<div class="field field-reserved">
    <select name="country" required>
        <option selected hidden value="">Choose country</option>
        <option value="ch">Switzerland</option>
        <option value="fr">France</option>
        <option value="de">Germany</option>
        <option value="nl">The Netherlands</option>
<div class="field field-reserved">
    <input type="text" name="zip" placeholder="Enter ZIP code" data-validate='{"zip": {}}' />
hyva.formValidation.addRule('zip', function(value, options, field, context) {
    const rules = {
        ch: ['^(CH-)?\\d{4}$', '<?= /* @noEscape */ __("Switzerland ZIPs must have exactly 4 digits: e.g. CH-1950 or 1950") ?>'],
        fr: ['^(F-)?\\d{5}$', '<?= /* @noEscape */ __("France ZIPs must have exactly 5 digits: e.g. F-75012 or 75012") ?>'],
        de: ['^(D-)?\\d{5}$', '<?= /* @noEscape */ __("Germany ZIPs must have exactly 5 digits: e.g. D-12345 or 12345") ?>'],
        nl: [
            '<?= /* @noEscape */ __("Netherland ZIPs must have exactly 4 digits, followed by 2 letters except SA, SD and SS") ?>'

    if (context.fields['country'].state.valid) {
        const country = context.fields['country'].element.value;
        const rule = new RegExp(rules[country][0], '');
        if (!rule.test(value)) {
            return rules[country][1];
        } else {
            return true;
    } else {
        return '<?= $escaper->escapeJs(__("Select country first")) ?>'

Custom non-error messages

Sometimes it is necessary to display additional messages besides validation failures.
This can be accomplished using the context.createMessage(field, messages) method.

The createMessage method can take a single message string or an array of messages.

The following example shows the number of characters remaining.
If more characters are added, the validation fails.

hyva.formValidation.addRule('remaining', (value, options, field, context) => {
    // Remove old message if present
    context.removeMessages(field, 'remaining-msg')

    const remaining = parseInt(options) - value.length;
    if (remaining < 0) {
        // Fail validation
        return hyva.strf('%0 character(s) too many', Math.abs(remaining));
    if (remaining > 0) {
        // Add message without failing validation
        const message = hyva.strf('<?= $escaper->escapeJs(__('%0 remaining')) ?>', remaining);
        context.addMessages(field, 'remaining-msg', message);
    return true;
<form x-data="hyva.formValidation($el)">
<div class="field field-reserved">
    <label for="example">Example</label>
    <textarea id="example" name="example" data-validate='{"remaining": 10}' @input="onChange"></textarea>