Allow to listen to the hidden event once

Expose an once event listener that allows
listening for the hidden event of tooltips

app/assets/javascripts/tooltips/components/tooltips.vue

@@ -82,9 +82,10 @@ export default {
     },
     triggerEvent(target, event) {
       const tooltip = this.findTooltipByTarget(target);
+      const tooltipRef = this.$refs[tooltip?.id];
 
-      if (tooltip) {
-        this.$refs[tooltip.id][0].$emit(event);
+      if (tooltipRef) {
+        tooltipRef[0].$emit(event);
       }
     },
     tooltipExists(element) {
@@ -113,6 +114,7 @@ export default {
       :boundary="tooltip.boundary"
       :disabled="tooltip.disabled"
       :show="tooltip.show"
+      @hidden="$emit('hidden', tooltip)"
     >
       <span v-if="tooltip.html" v-safe-html:[$options.safeHtmlConfig]="tooltip.title"></span>
       <span v-else>{{ tooltip.title }}</span>

app/assets/javascripts/tooltips/index.js

@@ -92,6 +92,7 @@ export const hide = createTooltipApiInvoker((element) =>
 export const show = createTooltipApiInvoker((element) =>
   tooltipsApp().triggerEvent(element, 'open'),
 );
+export const once = (event, cb) => tooltipsApp().$once(event, cb);
 export const destroy = () => {
   tooltipsApp().$destroy();
   app = null;

spec/frontend/tooltips/components/tooltips_spec.js

@@ -217,4 +217,14 @@ describe('tooltips/components/tooltips.vue', () => {
     wrapper.destroy();
     expect(observersCount()).toBe(0);
   });
+
+  it('exposes hidden event', async () => {
+    buildWrapper();
+    wrapper.vm.addTooltips([createTooltipTarget()]);
+
+    await wrapper.vm.$nextTick();
+
+    wrapper.findComponent(GlTooltip).vm.$emit('hidden');
+    expect(wrapper.emitted('hidden')).toHaveLength(1);
+  });
 });