Nuxtjs Guideline: Lifecycle — Use onMounted for DOM access. Description: Access DOM only after component is mounted. Do: onMounted for DOM manipulation. Don't: Direct DOM access in setup. Good Example: onMounted(() => { document.getElementById('el') }). Bad Example: <script setup>document.getElementById('el')</script>. Severity: High. Docs: https://nuxt.com/docs/api/composables/on-mounted.