feat(ktabs): add before change prop

docs/components/tabs.md

@@ -221,6 +221,80 @@ const tabChange = (hash: string): void => {
 </script>
 ```
 
+### beforeChange
+
+Prop that takes a function return value of which determines whether tab change should be skipped. Useful when some information needs to me brought to user's attention before they leave the content in the currently displayed tab.
+
+The function receives new tab value as an argument and returns a boolean value, `false` will prevent tab change. Defaults to `() => true`.
+
+<KTabs
+  :before-change="onBeforeTabChange"
+  :model-value="confirmedTab"
+  :tabs="tabs"
+>
+  <template #tab1>
+    Tab 1 content
+  </template>
+  <template #tab2>
+    Tab 2 content
+  </template>
+</KTabs>
+
+<KPrompt
+  message="Notice that the tab doesn't change until you've confirmed your action."
+  :visible="confirmPromptVisible"
+  @cancel="onCancel"
+  @proceed="onConfirm"
+/>
+
+```vue
+<template>
+  <KTabs
+    :before-change="onBeforeTabChange"
+    :model-value="activeTab"
+    :tabs="tabs"
+  >
+    <template #tab1>
+      Tab 1 content
+    </template>
+    <template #tab2>
+      Tab 2 content
+    </template>
+  </KTabs>
+
+  <KPrompt
+    message="Notice that the tab doesn't change until you've confirmed your action."
+    :visible="confirmPromptVisible"
+    @cancel="onCancel"
+    @proceed="onConfirm"
+  />
+</template>
+
+<script setup lang="ts">
+const activeTab = ref<string>('#tab1')
+const confirmPromptVisible = ref<boolean>(false)
+const targetTab = ref<string | null>(null)
+
+const onBeforeTabChange = (tab: string) => {
+  confirmPromptVisible.value = true
+  targetTab.value = tab
+
+  return false
+}
+
+const onConfirm = () => {
+  confirmPromptVisible.value = false
+  activeTab.value = targetTab.value!
+  targetTab.value = null
+}
+
+const onCancel = () => {
+  confirmPromptVisible.value = false
+  targetTab.value = null
+}
+</script>
+```
+
 ## Slots
 
 ### anchor & panel
@@ -351,6 +425,25 @@ const panelsActiveHash = ref('#gateway')
 const panelsChange = (hash: string) => {
   panelsActiveHash.value = hash;
 }
+
+const confirmedTab = ref<string>('#tab1')
+const confirmPromptVisible = ref<boolean>(false)
+const targetTab = ref<string | null>(null)
+const onBeforeTabChange = (tab: string) => {
+  confirmPromptVisible.value = true
+  targetTab.value = tab
+
+  return false
+}
+const onConfirm = () => {
+  confirmPromptVisible.value = false
+  confirmedTab.value = targetTab.value!
+  targetTab.value = null
+}
+const onCancel = () => {
+  confirmPromptVisible.value = false
+  targetTab.value = null
+}
 </script>
 
 <style lang="scss" scoped>

sandbox/pages/SandboxTabs.vue

@@ -66,6 +66,30 @@
           Tab 3 content
         </div>
       </SandboxSectionComponent>
+      <SandboxSectionComponent title="beforeChange">
+        <KTabs
+          :before-change="onBeforeTabChange"
+          :model-value="confirmedTab"
+          :tabs="items"
+        >
+          <template #tab1>
+            Tab 1 content
+          </template>
+          <template #tab2>
+            Tab 2 content
+          </template>
+          <template #tab3>
+            Tab 3 content
+          </template>
+        </KTabs>
+
+        <KPrompt
+          message="Notice that the tab doesn't change until you've confirmed your action."
+          :visible="confirmPromptVisible"
+          @cancel="onCancel"
+          @proceed="onConfirm"
+        />
+      </SandboxSectionComponent>
 
       <!-- Slots -->
       <SandboxTitleComponent
@@ -155,6 +179,7 @@ const items = [
 
 const vModel1 = ref<string>('#tab2')
 const vModel2 = ref<string>('#tab2')
+const confirmedTab = ref<string>('#tab1')
 
 const dynamicRouterViewItems = [
   {
@@ -168,4 +193,22 @@ const dynamicRouterViewItems = [
     to: { hash: '#two' },
   },
 ]
+
+const confirmPromptVisible = ref<boolean>(false)
+const targetTab = ref<string | null>(null)
+const onBeforeTabChange = (tab: string) => {
+  confirmPromptVisible.value = true
+  targetTab.value = tab
+
+  return false
+}
+const onConfirm = () => {
+  confirmPromptVisible.value = false
+  confirmedTab.value = targetTab.value!
+  targetTab.value = null
+}
+const onCancel = () => {
+  confirmPromptVisible.value = false
+  targetTab.value = null
+}
 </script>

src/components/KTabs/KTabs.cy.ts

@@ -126,6 +126,19 @@ describe('KTabs', () => {
     cy.get('.tab-item .tab-link').eq(1).should('not.have.attr', 'href')
   })
 
+  it('does not change the tab when beforeChange returns false', () => {
+    cy.mount(KTabs, {
+      props: {
+        tabs: TABS,
+        beforeChange: () => false,
+      },
+    })
+
+    cy.get('.tab-item').eq(1).click().then(() => {
+      cy.wrap(Cypress.vueWrapper.emitted()).should('not.have.property', 'change')
+    })
+  })
+
   describe('slots', () => {
     it('provides the #hash slot content', () => {
       const picturesSlot = 'I love pictures'

src/components/KTabs/KTabs.vue

@@ -87,6 +87,10 @@ const props = defineProps({
     default: 0,
     validator: (val: number): boolean => val >= -1 && val <= 32767,
   },
+  beforeChange: {
+    type: Function as PropType<(tab: string) => boolean>,
+    default: () => true,
+  },
 })
 
 const emit = defineEmits<{
@@ -97,9 +101,11 @@ const emit = defineEmits<{
 const activeTab = ref<string>(props.modelValue ? props.modelValue : props.tabs[0]?.hash)
 
 const handleTabChange = (tab: string): void => {
-  activeTab.value = tab
-  emit('change', tab)
-  emit('update:modelValue', tab)
+  if (props.beforeChange(tab)) {
+    activeTab.value = tab
+    emit('change', tab)
+    emit('update:modelValue', tab)
+  }
 }
 
 const getTabSlotName = (tabHash: string): string => tabHash.replace('#', '')