feat(ui): set focus on combobox when loaded

When Combobox is loaded in Datacenters and Infrastructures views, the
focus is automatically set on the input so user can directly type or
select an entry with keyboard without requiring an initial click on the
Combobox.

racksdb/web/ui/src/components/ComboBox.vue

@@ -5,7 +5,7 @@ This file is part of RacksDB.
 SPDX-License-Identifier: GPL-3.0-or-later -->
 
 <script setup lang="ts">
-import { ref, computed, watchEffect } from 'vue'
+import { ref, computed, watchEffect, onMounted } from 'vue'
 import type { Ref } from 'vue'
 import { useRouter } from 'vue-router'
 import type { Datacenter, Infrastructure } from '@/composables/RacksDBAPI'
@@ -21,6 +21,7 @@ import { ChevronUpDownIcon, CheckIcon } from '@heroicons/vue/24/outline'
 const selectedItem: Ref<string | undefined> = ref()
 const router = useRouter()
 const input = ref('')
+const inputComponent: Ref<typeof ComboboxInput | null> = ref(null)
 const filteredItem = computed(() =>
   input.value === ''
     ? props.items
@@ -52,13 +53,25 @@ watchEffect(() => {
     goToItem(selectedItem.value)
   }
 })
+
+onMounted(() => {
+  /*
+   * Give focus to ComboboxInputElement when component is loaded.
+   *
+   * This is not stated in Headless UI documentation but ComboboxInput
+   * component exposes an el attribute which is a ref on the child input
+   * HTML element. This can be use to set focus on this element.
+   */
+  inputComponent.value?.el.focus()
+})
 </script>
 
 <template>
   <div class="flex justify-center items-center pt-10">
     <Combobox as="div" v-model="selectedItem" class="p-4 px-20">
       <div class="relative mt-2">
         <ComboboxInput
+          ref="inputComponent"
           class="w-96 focus:border-purple-700 focus:outline-none border-2 border-solid rounded-md bg-white py-1.5 pl-3 pr-10 text-gray-900 shadow-sm ring-1 ring-inset ring-gray-300 focus:ring-2 focus:ring-inset focus:ring-purple-600 sm:text-sm sm:leading-6"
           placeholder="Filter a name"
           @change="input = $event.target.value"