Advanced forms with Alpine.js

Visualise validation errors in your backend for input elements with Alpine.js and improve the user experience of your forms. Read more in this article.

Jairus Joer

Jairus Joer

The texts in this article were partly composed with the help of artificial intelligence and corrected and revised by us. The following services were used for the generation:

If you are not yet familiar with working on forms with Alpine.js, you can refresh your knowledge in our first article on this topic, Interactive forms with Alpine.js.

In our first article on interactive forms with Alpine.js, we already indicated that Alpine.js can also be used to influence individual elements in addition to the general display of server-side information in the form.

Due to the popular demand, we have decided to take up precisely this topic in this follow-up article and show examples of how you can use information and states to validate a form with Alpine.js.


For this demonstration, we are using our Astro Boilerplate, which we have already presented in detail in an earlier article.

Download Astro Boilerplate

If our boilerplate isn’t right for you, that’s not a problem. The steps for validating form entries work in any project with Alpine.js.

Integrating methods for Alpine.js

In order to be able to access the required data and methods from Alpine.js in the further course of the implementation, these are first declared in order to avoid errors in the further course.


form() controls the loading state and saves the Response sent by the server via the submit() method, which is executed when the form is submitted.

A fictitious fakeResponse() is also included, which “receives” exemplary and simplified validation errors from our fictitious backend.

import { sleep } from "../utilities"

export const form = () => ({
  loading: false,
  response: null as unknown,

  async submit(event: SubmitEvent) {
    this.loading = true
    this.response = null
    const formData = new FormData( as HTMLFormElement)

     * Replace the following fake response with your `fetch` request and 
     * receive the validated results from the server side as JSON. 
     * Make sure you add the necessary attributes to the `<Input />' 
     * elements to perform client-side validation as well.

    const fakeResponse = async () => {
      await sleep(1000) // Mock response time

      return {
        errors: {
          // []: "message string"
          username: "Username is alrady taken",
          password: "Password is too short"

    this.response = await fakeResponse()
    this.loading = false

The Response must contain an error object in which each key-value pair consists of the name of the input element and the associated validation error.


input.ts handles the display of validation errors for an input element via the validate() method, which is integrated via the x-effect attribute in order to recalculate the data for display when the form is submitted.

export const input = () => ({
  error: null as unknown,

  validate() {
    if (!this.response?.errors?.[this.$]) return (this.error = null)
    this.error = this.response.errors[this.$]


Finally, the methods declared for Alpine.js are imported for this step and registered in the EventListener alpine:init in order to be able to access the required scopes.

import Alpine from "alpinejs"
import { app } from "./alpine/app"
import { form } from "./alpine/form"
import { input } from "./alpine/input"

// Await Alpine.js initialization
document.addEventListener("alpine:init", () => {"app", app)"form", form)"input", input)


Declaring optional utility methods

So that we can also use names for input elements as labels, we create the method capitalize, which splits strings written in kebab-case (e.g.: "email-address") and capitalises each word.

If you decide against capitalisation, the corresponding references in the input.astro component must be removed

export const capitalize = (string: string) => {
  return string.split("-").map(word => word[0].toUpperCase() + word.substring(1)).join(" ")

Creating pages and components in Astro

In the following step, we create the pages and components we need for the form. We define an <Input /> component and integrate it into the form block.


input.astro combines the elements <input /> and <label> in one component and also contains the representation of the validation errors, which are mapped via the Alpine context input.

import { capitalize } from "@/scripts/utilities"

const { name, ...props } = Astro.props

  class="relative font-medium" 
    class="absolute pointer-events-none overflow-hidden top-3 inset-x-4 flex gap-1 items-center leading-4 text-xs transition-colors" 
    x-bind:class="error && 'text-rose-500'"
      {capitalize(name)}{props?.required && '*'}
      class="ml-3 overflow-hidden flex justify-end gap-1" 
    class="w-full pt-7 pb-3 px-4 border rounded-xl leading-6 bg-transparent text-foreground invalid:border-rose-500 disabled:bg-muted transition-colors" 
    x-bind:class="error && 'border-rose-500'" 


index.astro represents our form block and uses the predefined component <Input /> and supplements its logic with the form context so that errors from the response object can be displayed.

While our component <Input /> handles the display of validation errors, we bind the disabled attribute of the individual input elements to the loading state in order to prevent multiple submissions of the form during processing.

import Root from "@/layouts/root.astro"
import Input from "@/components/input.astro"

const meta = {
  title: "Advanced forms with Alpine.js"

<Root {meta}>
      class="grid gap-2 p-6" 
        placeholder="[email protected]"
        placeholder="Your password"
        class="bg-primary text-primary-foreground h-12 rounded-xl font-medium disabled:opacity-50 transition-opacity"


With Alpine.js, we demonstrate how validation errors from the backend are dynamically displayed in a form and how input elements react to corresponding events in the browser.