<template>
  <input v-model="username" type="text" />
</template>

<script>
export default {
  data() {
    return {
      username: ''
    }
  }
}
</script>

<template>
  <nuxt-link to="/other-page">Go to Other Page</nuxt-link>
</template>

// plugins/preserve-input.js
import Vue from 'vue'

Vue.mixin({
  beforeRouteLeave(to, from, next) {
    this.$store.commit('preserveInputValues', this.$data)
    next()
  },
  beforeRouteEnter(to, from, next) {
    this.$store.dispatch('restoreInputValues', this)
    next()
  }
})