v-model Ignores Initial HTML Attributes

Impact: HIGH - Setting initial values via HTML value, checked, or selected attributes has no effect when using v-model. The form will appear empty or in an unexpected state, confusing users and potentially causing data loss.

Vue's v-model always treats the bound JavaScript state as the single source of truth. Any initial attributes in the HTML are completely ignored. This is a common mistake when migrating from plain HTML forms or when copying HTML templates.

Task Checklist

• [ ] Never rely on HTML value, checked, or selected attributes when using v-model
• [ ] Always declare initial values in JavaScript using ref() or reactive()
• [ ] When migrating plain HTML forms to Vue, move all default values to JavaScript state
• [ ] Audit existing forms for hardcoded HTML default values that may be silently ignored

Incorrect:

<script setup>
import { ref } from 'vue'

const username = ref('')  // Empty!
const isSubscribed = ref(false)  // Not checked!
const country = ref('')  // No default selection!
</script>

<template>
  <!-- WRONG: These HTML attributes are completely ignored -->
  <input v-model="username" value="default_user">

  <input type="checkbox" v-model="isSubscribed" checked>

  <select v-model="country">
    <option value="us" selected>United States</option>
    <option value="uk">United Kingdom</option>
  </select>
</template>

Correct:

<script setup>
import { ref } from 'vue'

// CORRECT: Set initial values in JavaScript
const username = ref('default_user')
const isSubscribed = ref(true)
const country = ref('us')
</script>

<template>
  <!-- HTML attributes not needed - JavaScript state controls everything -->
  <input v-model="username">

  <input type="checkbox" v-model="isSubscribed">

  <select v-model="country">
    <option value="us">United States</option>
    <option value="uk">United Kingdom</option>
  </select>
</template>

// Options API equivalent
export default {
  data() {
    return {
      username: 'default_user',
      isSubscribed: true,
      country: 'us'
    }
  }
}

Reference

• Vue.js Form Input Bindings