Implementing Custom Form Validators in Vue.js

1. Introduction

In this tutorial, we aim to guide you through the process of implementing custom form validators in Vue.js. Our main goal is to assist you in creating unique validation rules for specific needs.

By the end of this tutorial, you will learn how to:

• Create a Vue.js application
• Implement custom form validators in Vue.js
• Test your custom form validators

Prerequisites: A basic understanding of Vue.js and JavaScript is required. Ensure that you have Node.js and npm installed on your computer.

2. Step-by-Step Guide

Form validation is crucial for any interactive web application. It ensures that users provide the necessary information in the correct format before it is sent off.

Vue.js doesn't provide built-in form validation, but we can create our custom validators quite easily. We'll use Vuelidate, a lightweight model-based validation for Vue.js.

Step 1: Create a Vue.js Application

First, we need to set up a new Vue.js application. If Vue CLI is not installed, you can install it using npm:

npm install -g @vue/cli

Next, create a new Vue.js project:

vue create vue-form-validation

Step 2: Install Vuelidate

Navigate into your new project and install Vuelidate:

cd vue-form-validation
npm install vuelidate --save

Step 3: Import and Use Vuelidate

In your main.js file, import and use Vuelidate:

import Vue from 'vue'
import Vuelidate from 'vuelidate'
Vue.use(Vuelidate)

3. Code Examples

Let's create a simple form with a custom validator that checks whether the input is a palindrome.

<template>
  <div>
    <form @submit.prevent="submitForm">
      <input v-model="word" type="text" placeholder="Enter a word">
      <span v-if="!$v.word.palindrome">Not a palindrome</span>
      <button type="submit">Submit</button>
    </form>
  </div>
</template>

<script>
import { validationMixin } from 'vuelidate'
import { required, helpers } from 'vuelidate/lib/validators'

export default {
  mixins: [validationMixin],
  data () {
    return {
      word: '',
    }
  },
  validations: {
    word: {
      required,
      palindrome: helpers.withMessage(
        'Must be a palindrome',
        value => value === value.split('').reverse().join('')
      )
    }
  },
  methods: {
    submitForm () {
      this.$v.$touch()
      if (this.$v.$invalid) {
        // handle error
      } else {
        // form is valid, continue...
      }
    }
  }
}
</script>

4. Summary

In this tutorial, you learned:

• How to create a new Vue.js application
• Installing and using Vuelidate
• How to implement custom form validators

To further your learning, consider exploring other features provided by Vuelidate, such as asynchronous validation and collection validation.

5. Practice Exercises

1. Create a form with a custom validator that checks if an email is in the correct format (Hint: use regex).
2. Create a form with a custom validator that checks if a password is at least 8 characters long and contains at least one number and one special character.
3. Create a form with a custom validator that checks if a date entered is in the future.

Don't forget to test your validators and ensure they are working as expected. Happy coding!