Vue.js: Formulários e v-model

<!-- v-model is props + emit syntax sugar -->
<input v-model="searchQuery">

<!-- equivalent to -->
<input 
  :value="searchQuery" 
  @input="searchQuery = $event.target.value"
>

<!-- Using Parent Components v-model -->
<CustomInput v-model="searchQuery" />

<!-- equivalent to -->
<CustomInput 
  :modelValue="searchQuery" 
  @update:modelValue="searchQuery = $event"
/>

<!-- 1. text input -->
<input v-model="text">

<!-- 2. textarea -->
<textarea v-model="description"></textarea>

<!-- 3. checkbox -->
<input v-model="agreed" type="checkbox">

<!-- 4. radio -->
<input v-model="gender" type="radio" value="male">
<input v-model="gender" type="radio" value="female">

<!-- 5. select -->
<select v-model="selected">
  <option value="vue">Vue</option>
  <option value="react">React</option>
</select>

Digitar no input atualiza text linha a linha.
Marcar o checkbox → agreed = true; escolher female → gender = 'female'.
Selecionar Vue no select → selected = 'vue' (valor da option).

<!-- Parent Component:v-model.trim -->
<CustomInput v-model.trim="username" />

<!-- Child component:Processing trim Modifiers -->
<script setup>
const props = defineProps({
  modelValue: String,
  modelModifiers: { default: () => ({}) }
})
const emit = defineEmits(['update:modelValue'])

function onInput(e) {
  let value = e.target.value
  if (props.modelModifiers.trim) {
    value = value.trim()
  }
  emit('update:modelValue', value)
}
</script>

O pai escreve <CustomInput v-model="search" />.
Digitar no filho emite update:modelValue e search é atualizado no pai.
É o mesmo que :modelValue="search" mais @update:modelValue="search = $event".

// utils/validators.js
export function isEmail(value) {
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(value)
}

export function isPhone(value) {
  return /^1[3-9]\d{9}$/.test(value)
}

export function minLength(value, min) {
  return value.length >= min
}

<template>
  <form @submit.prevent="handleSubmit">
    <input v-model="form.email" @blur="validateField('email')">
    <p v-if="errors.email" class="error">{{ errors.email }}</p>
    
    <input v-model="form.password" type="password">
    <p v-if="errors.password">{{ errors.password }}</p>
    
    <button :disabled="!isValid">Submit</button>
  </form>
</template>

<script setup>
import { reactive, ref } from 'vue'
import { isEmail, minLength } from '@/utils/validators'

const form = reactive({
  email: '',
  password: ''
})

const errors = reactive({})
const isValid = ref(false)

function validateField(field) {
  if (field === 'email') {
    if (!form.email) {
      errors.email = 'Email is required'
    } else if (!isEmail(form.email)) {
      errors.email = 'Invalid email format'
    } else {
      delete errors.email
    }
  }
  
  if (field === 'password') {
    if (!form.password) {
      errors.password = 'Password is required'
    } else if (!minLength(form.password, 8)) {
      errors.password = 'Password must be 8+ characters'
    } else {
      delete errors.password
    }
  }
  
  isValid.value = Object.keys(errors).length === 0
}

function handleSubmit() {
  Object.keys(form).forEach(validateField)
  if (isValid.value) {
    console.log('Submit:', form)
  }
}
</script>

npm install vee-validate @vee-validate/rules

<template>
  <Form @submit="handleSubmit" :validation-schema="schema">
    <Field name="email" type="email" v-model="form.email" />
    <ErrorMessage name="email" />
    
    <Field name="password" type="password" v-model="form.password" />
    <ErrorMessage name="password" />
    
    <button>Submit</button>
  </Form>
</template>

<script setup>
import { Form, Field, ErrorMessage } from 'vee-validate'
import * as yup from 'yup'

const schema = yup.object({
  email: yup.string().email().required(),
  password: yup.string().min(8).required()
})

const form = reactive({ email: '', password: '' })

function handleSubmit(values) {
  console.log('Valid:', values)
}
</script>

// 1. Required
if (!form.email) errors.email = 'Required'

// 2. Email
if (!isEmail(form.email)) errors.email = 'Invalid email'

// 3. Cell Phone
if (!isPhone(form.phone)) errors.phone = 'Invalid phone'

// 4. Length
if (form.password.length < 8) errors.password = 'Too short'

// 5. Confirm Password
if (form.password !== form.confirm) errors.confirm = 'Mismatch'

Formulário vazio → errors recebe Required em email e as demais mensagens.
Email malformado mostra Invalid email; telefone inválido mostra Invalid phone.
Senha com menos de 8 caracteres → Too short; confirmação diferente → Mismatch.

const form = reactive({
  user: {
    name: '',
    email: '',
    age: 0
  },
  address: {
    city: '',
    country: ''
  }
})

const form = reactive({
  items: [
    { name: '', quantity: 1, price: 0 }
  ]
})

function addItem() {
  form.items.push({ name: '', quantity: 1, price: 0 })
}

function removeItem(index) {
  form.items.splice(index, 1)
}

<!-- 1. .lazy:change Event Trigger(No input) -->
<input v-model.lazy="email">

<!-- 2. .number:Automatically Convert to Numbers -->
<input v-model.number="age" type="number">

<!-- 3. .trim:Automatically Remove Spaces -->
<input v-model.trim="username">

<!-- 4. Custom Modifiers(CustomInput) -->
<CustomInput v-model.trim="text" />

<!-- 5. .debounce(Custom):300ms Image Stabilization -->
<DebouncedInput v-model:debounce="500" />

<!-- 1. .lazy:change Event -->
<input v-model.lazy="email">

<!-- 2. .number:Automatically Convert to Numbers -->
<input v-model.number="age" type="number">

<!-- 3. .trim:Automatic trim -->
<input v-model.trim="username">

<!-- 4. Combinations of Multiple Modifiers -->
<input v-model.lazy.trim="email">

<!-- 5. Custom Modifiers(Child component)-->
<CustomInput v-model.trim="text" />

.lazy só atualiza o dado no evento change (ao sair do campo).
.number converte o texto digitado em número; .trim remove os espaços das pontas.
Em componentes, os modificadores chegam ao filho em defineModel() ou modelModifiers.