Nuxt/examples/async-data/pages/index.vue

<template>
  <div class="container">
    <h1>User Agent</h1>
    <p>{{ userAgent }}</p>
    <p>
      <NuxtLink to="/posts">
        Blog
      </NuxtLink>
    </p>
  </div>
</template>

<script>
export default {
  asyncData: ({ req }) => ({
    userAgent: (req ? req.headers['user-agent'] : (typeof navigator !== 'undefined' ? navigator.userAgent : 'No user agent (generated)'))
  })
}
</script>

<style scoped>
.container {
  width: 70%;
  margin: auto;
  text-align: center;
  padding-top: 100px;
}
p {
  font-size: 20px;
}
a {
  color: #41B883;
}
</style>