Automatically focus cluster dropdown search box

app/assets/javascripts/create_cluster/eks_cluster/components/cluster_form_dropdown.vue

 <script>
+import $ from 'jquery';
 import { GlIcon } from '@gitlab/ui';
 import DropdownSearchInput from '~/vue_shared/components/dropdown/dropdown_search_input.vue';
 import DropdownHiddenInput from '~/vue_shared/components/dropdown/dropdown_hidden_input.vue';
@@ -106,6 +107,7 @@ export default {
   data() {
     return {
       searchQuery: '',
+      focusOnSearch: false,
     };
   },
   computed: {
@@ -141,6 +143,18 @@ export default {
       return itemsProp(this.selectedItems, this.valueProperty).join(', ');
     },
   },
+  mounted() {
+    $(this.$refs.dropdown)
+      .on('shown.bs.dropdown', () => {
+        this.focusOnSearch = true;
+      })
+      .on('hidden.bs.dropdown', () => {
+        this.focusOnSearch = false;
+      });
+  },
+  beforeDestroy() {
+    $(this.$refs.dropdown).off();
+  },
   methods: {
     getItemsOrEmptyList() {
       return this.items || [];
@@ -170,7 +184,7 @@ export default {
 
 <template>
   <div>
-    <div class="js-gcp-machine-type-dropdown dropdown">
+    <div ref="dropdown" class="dropdown">
       <dropdown-hidden-input :name="fieldName" :value="selectedItemsValues" />
       <dropdown-button
         :class="{ 'border-danger': hasErrors }"
@@ -179,7 +193,11 @@ export default {
         :toggle-text="toggleText"
       />
       <div class="dropdown-menu dropdown-select">
-        <dropdown-search-input v-model="searchQuery" :placeholder-text="searchFieldPlaceholder" />
+        <dropdown-search-input
+          v-model="searchQuery"
+          :focused="focusOnSearch"
+          :placeholder-text="searchFieldPlaceholder"
+        />
         <div class="dropdown-content">
           <ul>
             <li v-if="!results.length">

app/assets/javascripts/vue_shared/components/dropdown/dropdown_search_input.vue

@@ -8,6 +8,11 @@ export default {
       required: true,
       default: __('Search'),
     },
+    focused: {
+      type: Boolean,
+      required: false,
+      default: false,
+    },
   },
   data() {
     return { searchQuery: this.value };
@@ -16,6 +21,11 @@ export default {
     searchQuery(query) {
       this.$emit('input', query);
     },
+    focused(val) {
+      if (val) {
+        this.$refs.searchInput.focus();
+      }
+    },
   },
 };
 </script>
@@ -23,6 +33,7 @@ export default {
 <template>
   <div class="dropdown-input">
     <input
+      ref="searchInput"
       v-model="searchQuery"
       :placeholder="placeholderText"
       class="dropdown-input-field"

changelogs/unreleased/36326-auto-focus-search-bar.yml

+---
+title: Autofocus cluster dropdown search input
+merge_request: 21440
+author:
+type: changed

spec/frontend/create_cluster/eks_cluster/components/cluster_form_dropdown_spec.js

 import { shallowMount } from '@vue/test-utils';
+import $ from 'jquery';
 
 import { GlIcon } from '@gitlab/ui';
 import ClusterFormDropdown from '~/create_cluster/eks_cluster/components/cluster_form_dropdown.vue';
@@ -169,4 +170,14 @@ describe('ClusterFormDropdown', () => {
     expect(vm.findAll('.js-dropdown-item').length).toEqual(1);
     expect(vm.find('.js-dropdown-item').text()).toEqual(secondItem.name);
   });
+
+  it('focuses dropdown search input when dropdown is displayed', () => {
+    const dropdownEl = vm.find('.dropdown').element;
+
+    expect(vm.find(DropdownSearchInput).props('focused')).toBe(false);
+
+    $(dropdownEl).trigger('shown.bs.dropdown');
+
+    expect(vm.find(DropdownSearchInput).props('focused')).toBe(true);
+  });
 });

spec/frontend/vue_shared/components/dropdown/dropdown_search_input_spec.js

+import { mount } from '@vue/test-utils';
+import DropdownSearchInputComponent from '~/vue_shared/components/dropdown/dropdown_search_input.vue';
+
+describe('DropdownSearchInputComponent', () => {
+  let wrapper;
+
+  const defaultProps = {
+    placeholderText: 'Search something',
+  };
+  const buildVM = (propsData = defaultProps) => {
+    wrapper = mount(DropdownSearchInputComponent, {
+      propsData,
+    });
+  };
+  const findInputEl = () => wrapper.find('.dropdown-input-field');
+
+  beforeEach(() => {
+    buildVM();
+  });
+
+  afterEach(() => {
+    wrapper.destroy();
+  });
+
+  describe('template', () => {
+    it('renders input element with type `search`', () => {
+      expect(findInputEl().exists()).toBe(true);
+      expect(findInputEl().attributes('type')).toBe('search');
+    });
+
+    it('renders search icon element', () => {
+      expect(wrapper.find('.fa-search.dropdown-input-search').exists()).toBe(true);
+    });
+
+    it('renders clear search icon element', () => {
+      expect(wrapper.find('.fa-times.dropdown-input-clear.js-dropdown-input-clear').exists()).toBe(
+        true,
+      );
+    });
+
+    it('displays custom placeholder text', () => {
+      expect(findInputEl().attributes('placeholder')).toBe(defaultProps.placeholderText);
+    });
+
+    it('focuses input element when focused property equals true', () => {
+      const inputEl = findInputEl().element;
+
+      jest.spyOn(inputEl, 'focus');
+
+      wrapper.setProps({ focused: true });
+
+      expect(inputEl.focus).toHaveBeenCalled();
+    });
+  });
+});

spec/javascripts/vue_shared/components/dropdown/dropdown_search_input_spec.js

-import Vue from 'vue';
-
-import mountComponent from 'spec/helpers/vue_mount_component_helper';
-import dropdownSearchInputComponent from '~/vue_shared/components/dropdown/dropdown_search_input.vue';
-
-const componentConfig = {
-  placeholderText: 'Search something',
-};
-
-const createComponent = (config = componentConfig) => {
-  const Component = Vue.extend(dropdownSearchInputComponent);
-
-  return mountComponent(Component, config);
-};
-
-describe('DropdownSearchInputComponent', () => {
-  let vm;
-
-  beforeEach(() => {
-    vm = createComponent();
-  });
-
-  afterEach(() => {
-    vm.$destroy();
-  });
-
-  describe('template', () => {
-    it('renders input element with type `search`', () => {
-      const inputEl = vm.$el.querySelector('input.dropdown-input-field');
-
-      expect(inputEl).not.toBeNull();
-      expect(inputEl.getAttribute('type')).toBe('search');
-    });
-
-    it('renders search icon element', () => {
-      expect(vm.$el.querySelector('.fa-search.dropdown-input-search')).not.toBeNull();
-    });
-
-    it('renders clear search icon element', () => {
-      expect(
-        vm.$el.querySelector('.fa-times.dropdown-input-clear.js-dropdown-input-clear'),
-      ).not.toBeNull();
-    });
-
-    it('displays custom placeholder text', () => {
-      const inputEl = vm.$el.querySelector('input.dropdown-input-field');
-
-      expect(inputEl.getAttribute('placeholder')).toBe(componentConfig.placeholderText);
-    });
-  });
-});