Return early when using `router.on()` during SSR

[RobertBoes]

When using router.on() it is always executed, this means the following won't work during SSR:

<script setup>
import { router } from '@inertiajs/vue3'

router.on('start', (event) => {
  console.log(`Starting a visit to ${event.detail.visit.url}`)
})
</script>

Instead, we'd need to wrap this in a onMounted hook, or check if the document/window exists;

<script setup>
import { router } from '@inertiajs/vue3'
import { onMounted } from 'vue'

onMounted(() => {
  router.on('start', (event) => {
    console.log(`Starting a visit to ${event.detail.visit.url}`)
  })
})
</script>

But since router.on() is already just a wrapper for document.addEventListener() I'd expect the wrapper to take care of that for you.

A simple fix I've made here is to simply check if we're in ssr with the isServer constant, if it is we return an empty void function