fix(timeline): fix NTimeline header slot (#706)

Co-authored-by: 07akioni <07akioni2@gmail.com>

CHANGELOG.en-US.md

@@ -7,6 +7,7 @@
 ### Fixes
 
 - Fix `n-message`'s `destroyAll` method doesn't work.
+- Fix `n-timeline`'s header slot is invalid when using alone.
 
 ## 2.15.9 (2021-07-28)
 

CHANGELOG.zh-CN.md

@@ -7,6 +7,7 @@
 ### Fixes
 
 - 修复 `n-message` 的 `destroyAll` 方法不生效
+- 修复 `n-timeline` 的 header slot 单独使用无效的问题
 
 ## 2.15.9 (2021-07-28)
 

src/timeline/src/TimelineItem.tsx

@@ -88,7 +88,7 @@ export default defineComponent({
           <div class={`${mergedClsPrefix}-timeline-item-timeline__circle`} />
         </div>
         <div class={`${mergedClsPrefix}-timeline-item-content`}>
-          {this.title ? (
+          {this.title || this.$slots.header ? (
             <div class={`${mergedClsPrefix}-timeline-item-content__title`}>
               {renderSlot(this.$slots, 'header', undefined, () => [this.title])}
             </div>

src/timeline/tests/Timeline.spec.ts

@@ -90,12 +90,16 @@ describe('n-timeline-item', () => {
       slots: {
         default: () =>
           h(NTimelineItem, null, {
-            default: () => 'test-default',
             header: () => 'test-header',
+            default: () => 'test-default',
             footer: () => 'test-footer'
           })
       }
     })
+    expect(wrapper.find('.n-timeline-item-content__title').exists()).toBe(true)
+    expect(wrapper.find('.n-timeline-item-content__title').text()).toBe(
+      'test-header'
+    )
     expect(wrapper.find('.n-timeline-item-content__content').exists()).toBe(
       true
     )