“document is not defined” in Nuxt.js

It’s a common error when you start a Nuxt project 😉

The Choices.js lib is available only for client-side! So Nuxt tried to renderer from server-side, but from Node.js window.document doesn’t exist, then you have an error.
nb: window.document is only available from the browser renderer.

Since Nuxt 1.0.0 RC7, you can use <no-ssr> element to allow your component only for client-side.

<template>
  <div>
    <no-ssr placeholder="loading...">
      <your-component>
    </no-ssr>
  </div>
</template>

take a look at the official example here: https://github.com/nuxt/nuxt.js/blob/dev/examples/no-ssr/pages/index.vue

Update:

Since Nuxt >= 2.9.0, you have to use the <client-only> element instead of <no-ssr>:

<template>
  <div>
    <client-only placeholder="loading...">
      <your-component>
    </client-only>
  </div>
</template>

To know more, see nuxt docs: https://nuxtjs.org/docs/2.x/features/nuxt-components#the-client-only-component