How to react to route changes on Vue 3, "script setup" composition API?

Question

This is an example of routes I have in my application:

{
  path: "/something",
  name: "SomeRoute",
  component: SomeComponent,
  meta: {showExtra: true},
},
{
  path: "/somethingElse",
  name: "SomeOtherRoute",
  component: SomeOtherComponent,
},

Then I have the following component, which as you will notice has two script tags, one with composition API, one without:

<template>
  <div>
    This will always be visible. Also here's a number: {{ number }}
  </div>

  <div v-if="showExtra">
    This will be hidden in some routes.
  </div>
</template>

<script setup lang="ts">
import type { RouteLocationNormalized } from "vue-router"
import { ref } from "vue"

const number = 5
const showExtra = ref(true)

const onRouteChange = (to: RouteLocationNormalized) => {
  showExtra.value = !!to.meta?.showExtra
}
</script>

<script lang="ts">
import { defineComponent } from "vue"


export default defineComponent({
  watch: {
    $route: {
      handler: "onRouteChange",
      flush: "pre",
      immediate: true,
      deep: true,
    },
  },
})
</script>

This works correctly: when I enter a route with meta: {showExtra: false} it hides the extra div, otherwise it shows it.

What I want to do, however, is achieve the same by only using the composition API, in other words removing the second <script> tag entirely. I have tried this:

<script setup lang="ts">
import type { RouteLocationNormalized } from "vue-router"
import { ref } from "vue"
import { onBeforeRouteUpdate } from "vue-router"


// ...
// same as before
// ...

onBeforeRouteUpdate(onRouteChange)
</script>

But this won't take effect as expected when I switch route. I'm aware of the watch function I could import, but I'm unsure how to get the meta information about the route and how to appease the type checker.

Answer 1

You can convert your watcher to composition api by importing watch method from vue

<script lang="ts">
import { defineComponent, vue, watch } from "vue"
import { useRoute } from "vue-router"

export default defineComponent({
  setup() {
    const route = useRoute()
    watch(route, (to) => {
      showExtra.value = !!to.meta?.showExtra
    }, {flush: 'pre', immediate: true, deep: true})
  },
})
</script>