AlpineJS Plugin — Simple Form Validation

Very simple form validation plugin for AlpineJS. This plugin is designed, like AlpineJS itself, to be sprinkled in as needed. What this plugin does not do is impose an opinionated structure for your form data or functionality. It can be used with or without x-model.

The x-validate directive allows for simple validation and error display. It also captures all form data in a reactive formData. The $validate magic function grants access to validation functions, formData, and simple submit validation check.

Update 1.8

Works with nested fieldsets for $validate magic functions like isComplete(), data(), or value().
Disabled is now a field property of the formData object. When a field is disabled, either by setting disabled on the field itself or a parent fieldset, the disabled property is set to true. Disabled fields are valid by default and return no value. Disabled is watched for by a mutation observer so AlpineJS binding of :disabled will work.
Hidden attributes no longer require x-validate in order to update when set with :value or other javascript that dynamically updates the value. The mutation observer automatically spots the change and updates.
BREAKING CHANGE x-required is removed. Use AlpineJS binding :required instead to set the required dynamically.

Simple Usage

Add a x-data, and x-validate to your <form> element (you don't need any variables on x-data ; it just needs to be initiated as an Alpine component). This automatically:

Captures all data to a reactive formData[form] array which updates on blur or click (depending on field type).
Validates onblur using basic browser checkValidity() checking required attribute and input types.
Uses built-in improved regex validation for required, email, tel, and url type fields, since the browser versions are limited.
Automatically adds a hidden span.error-msg with error message adjacent to the field.
- You will need to style this yourself (see Example below)
When the validity check fails, it...
- Adds aria-invalid="true" and aria-errormessage attributes to the field element.
- Reveals the error message in by removing the hidden attribute.
- Also adds a superfluous data-error="{error message}" on the field's parent element for any additional styling you may want (searches for closest field-parent class parent element or failing that uses .parentNode).
- After blur triggers invalid, it adds 'input' event listener for validation as well as 'blur'
If valid is triggered, it reverses all the above
Use :disabled="$validate.isComplete('formId')" to disable submit button and/or use @submit="$validate.submit" to automatically check validity of all fields prior to submitting.

Custom Usage

Use x-validate directive along with modifiers directly on form fields to add additional validation, such as x-validate.wholenumber
Write a custom error message one of two ways:
- Add data-error-msg='custom error message' on field itself
- Add a sibling element with error-msg class and write your own error message there. The plugin searches all next siblings and will add the proper aria-errormessage with linked id tags for you. This is also useful if you want some descriptive text or other element before the error message or if you want to use special styling to a specific error message.
- Add an element with the correct id attribute anywhere on the page (id is error-msg-${id of matching field}) and it will use that.
Use x-validate.group on groups of checkboxes or radio buttons to validate that at least one is selected.
Add a specific test to a field like x-validate='$el.value === 'bunny' (see Using Expressions for Validation below).
Use $validate.isComplete(el) to detect if the form, <fieldset> groups or any field is completed
You can an skip x-validate on the <form> and just add x-validate on fields directly if you only want a couple fields validated. The x-data is still required on <form>.
The examples folder in the git repo shows some of what you can do with this plugin.

Directive x-validate

Form Element Directives and UI Modifiers

The UI modifiers are mainly for setting global defaults on <form> but you can also be used on individual form field elements for more specific control.

x-validate triggers validation and captures formData for entire form
x-validate.bluronly — change the default never to use 'input' event listener on fillable form fields
x-validate.input sets fields to use both 'blur' and 'input' event listener for all validation
x-validate.refocus sets fields to force focus on form element when invalid
x-validate.use-browser use the browser's built in validation as well as x-validate
x-validate.validate-on-submit automatically trigger validation on submit

Field Element Directives

These are bonus directives for built in regex validation. You can also ignore these and use the pattern attribute with your own regex.

Used on <input>, <select>, <textarea>

x-validate — only captures data; Useful on it's own if not set on <form>. Also useful with paired with an expression for specific field validation like x-validate='$el.value === 'bunny'. Note that in many cases the normal pattern attribute may be all you need.
x-validate.required — replacement for required attribute *
x-validate.tel - works the same as type='tel' using improved regex *
x-validate.email - works the same as type='email' using improved regex *
x-validate.website — valid if site domain, with or without http:// or https://
x-validate.url — works the same as type='url' using improved regex *
x-validate.number — valid if number (positive or negative; integer or decimal)
x-validate.integer — valid if integer number (positive or negative)
x-validate.wholenumber — valid if whole number (positive integer)
Date validation: allows for / or - or . between units
- x-validate.date defaults to 'yyyy-mm-dd' format, as that is what type='date' input field saves the date as
- x-validate.date.mmddyyyy — 'mm-dd-yyyy' format
- x-validate.date.ddmmyyyy — 'dd-mm-yyyy' format
- x-validate.date.yyyymmdd — 'yyyy-mm-dd' format
- If you want more complicated validation I recommend dayjs

* this allows you to use x-validate.required instead of required attribute or x-validate.tel on type='text' instead of type='tel'

Using Expressions for Validation

You can add a specific test to a field like x-validate='$el.value === 'bunny'; this can be paired up with other validations. For example: x-validate.website='$el.includes('bunny') for only websites with the word bunny in the name. Note that in many cases the normal pattern attribute may be all you need.

Checkbox and Radio Button Groups

Checkboxes and radio buttons that share the same name attribute update the same formData field data object. Radio buttons update the value with the currently selected button. Checkboxes save as both a comma separated string value and as an array.

You can validate that at least one is selected by adding x-validate.group to every checkbox or radio button in a named group. If you want the user to select multiple checkboxes, use an added expression with the minimum number x-validate.group="2".

Note: Checkbox and radio button groups add their error message after the wrapper for the group. This is either the closest field-parent class parent element or it uses .parentNode.parentNode by default. It's assumed that each checkbox/radio is wrapped in a label or list item, and then has a wrapper around the group.

Magic functions

$formData returns the formData object for the current form
$validate is an object with a group of functions (see functions below)

Validation Functions

You can add any specific validation like email or tel. Main difference between the magic function and the directive is that required is assumed.

both $validate.email('') and $validate.email('hi') returns false
$validate.email('hi@hello.com') returns true
val === '' || $validate.email(val) returns true if val is empty string or is a valid email address
validating the date allows formats as such $validate.date.mmddyyyy(str)

Other Functions

When used on <form>, the x-validate every field is added to a reactive formData[formId] array. If only used on individual fields, x-validate only adds those fields to the formData[formId] array.

@submit="$validate.submit" used on form element. Validates current form; if validation fails errors are shown and the submit event is prevented.
$validate.isComplete(el) returns true or false validity for form, fieldsets, or fields. *
$validate.data(el) returns an array of form or fieldset fields, or an individual field data object *
$validate.formData(form) returns the raw formData object with keyed field names *
$validate.value(el,value) returns a simple object with field names keys and their values for forms and fieldsets or just the raw value for fields. Value argument is optional and only for fields; when provided it will update the field value and update the x-validate formData. *

* 'el' argument variable works with either $refs or a string of the name/id for getting data from form, fieldset, and fields.

Advanced Functions

These grant access to some of the backend functions — use at your own risk.

$validate.updateData(field,data,triggerErrorMsg) allows you to directly add/update the formData array for a field. When called with just the field name it will grab the new value for the field. This is useful if you are updating the field dynamically via other javascript functions.
$validate.toggleError(field,valid) allows you to toggle the error message on any field.

Example formData

{
    'field-name': {
        name: 'field-name', node: [field HTMLElement], value: 'field value', valid: true, required: true, mods: [array of directive modifiers], set: [parent fieldset HTMLElement], parentNode: [parent HTMLElement], array: [array of checked selections (only used groups of checkboxes or radio buttons)], exp: [expression on x-validate]
    }
}

Note: name = name attribute || id attribute

Example

More complicated examples in examples folder. run npm run serve to view.

<form id="form" x-data x-validate.validate-on-submit action="/api/end-point" method="post">
        <p><em>* required</em></p>
        <div>
            <label for="name">Your Name *</label>
            <input type="text" id="name" name="name" required />
        </div>
        <div>
            <label for="email">Your Email *</label>
            <input type="email" id="email" name="email" required />
        </div>
        <div>
            <label for="wholenumber">Whole Number</label>
            <input type="wholenumber" id="wholenumber" name="wholenumber" x-validate.wholenumber data-error-msg="positive whole number required" />
        </div>
        <div id="animals" data-error-msg="you must pick at least one animal">
            <h4>Favorite Animals *</h4>
            <label><input type="checkbox" x-validate.group name="animal" id="cat" value="cat" /> 
                Cat</label>
            <label><input type="checkbox" x-validate.group name="animal" id="dog" value="dog" /> 
                Dog</label>
            <label><input type="checkbox" x-validate.group name="animal" id="bunny" value="bunny" /> 
                Bunny</label>
        </div>
        <div>
            <input type="submit" value="submit">
        </div>
    </form>
<style type="text/css">
    /* style to display the error message */
    .error-msg {
        color: red;
    }
</style>

The above example will validate using x-validate prior to submitting. If you need to submit using javascript, then you can use alpine for this as such:

<form id="form" x-data x-validate.validate-on-submit 
  @submit.prevent="if ($validate.isComplete('form')) yourPostFormFunctionHere($validate.value('form'))" >

Example of more elaborate error message styling

.error-msg[hidden] {
    opacity: 0;
    height: 0px;
    transform: scale(0);
}
.error-msg {
    font-size: 0.8rem;
    font-weight: 700;
    color: darkred;
    transform-origin: left;
    transition: all 200ms;
    display: block;
}

Installation

CDN

<script defer src="https://unpkg.com/@colinaut/alpinejs-plugin-simple-validate@1/dist/alpine.validate.min.js"></script>
<script defer src="https://unpkg.com/alpinejs@3.x.x/dist/cdn.min.js"></script>

NPM/PNPM/YARN

npm i @colinaut/alpinejs-plugin-simple-validate

pnpm i @colinaut/alpinejs-plugin-simple-validate

yarn add @colinaut/alpinejs-plugin-simple-validate

Bundling and initializing

If you are bundling your javascript then you can initialize the plugin like so:

import Alpine from "alpinejs";
import validate from "@colinaut/alpinejs-plugin-simple-validate";

Alpine.plugin(validate);

window.Alpine = Alpine;

Alpine.start();

Eleventy static site

If you are using Eleventy, and want to install locally rather than rely on the CDN, you can install via NPM/PNPM/YARN and then pass through the js file so that it is included in the output. Then you would just need to add it to the head.

eleventyConfig.addPassthroughCopy({
    "node_modules/alpinejs/dist/cdn.min.js" : "js/alpine.min.js",
    "node_modules/@colinaut/alpinejs-plugin-simple-validate/dist/alpine.validate.min.js": "js/alpine.validate.min.js",
})

<script src="/js/alpine.validate.min.js" defer></script>
<script src="/js/alpine.min.js" defer></script>

Roadmap

Clean up the code more.
Fix issue where fields get added error message even when they are not required.
Maybe add x-value to allow easier updating of values dynamically?

Feel free to add any enhancement requests on github.

Acknowledgements

Built using AlpineJS plugin blueprint

colinaut / alpinejs-plugin-simple-validate