fix(date-picker): undefined dayIndex (#2545)

docs/components/date-picker/DatePicker.vue

@@ -32,6 +32,11 @@ const attrs = {
   'is-dark': { selector: 'html', darkClass: 'dark' },
   'first-day-of-week': 2
 }
+
+function onDayClick(_: any, event: MouseEvent): void {
+  const target = event.target as HTMLElement
+  target.blur()
+}
 </script>
 
 <template>
@@ -40,11 +45,13 @@ const attrs = {
     v-model.range="date"
     :columns="2"
     v-bind="{ ...attrs, ...$attrs }"
+    @dayclick="onDayClick"
   />
   <VCalendarDatePicker
     v-else
     v-model="date"
     v-bind="{ ...attrs, ...$attrs }"
+    @dayclick="onDayClick"
   />
 </template>