cap virtual scroll index before use

src/components/timeline/timeline.js

@@ -158,6 +158,7 @@ const Timeline = {
       if (!this.virtualScrollingEnabled) return
 
       const statuses = this.$refs.timeline.children
+      const cappedScrollIndex = Math.max(0, Math.min(this.virtualScrollIndex, statuses.length - 1))
 
       if (statuses.length === 0) return
 
@@ -173,12 +174,9 @@ const Timeline = {
       // if we have a previous scroll index that can be used, test if it's
       // closer than the previous approximation, use it if so
 
-      const virtualScrollIndexY = statuses[this.virtualScrollIndex].getBoundingClientRect().y
-      if (
-        this.virtualScrollIndex < statuses.length &&
-        Math.abs(err) > virtualScrollIndexY
-      ) {
-        approxIndex = this.virtualScrollIndex
+      const virtualScrollIndexY = statuses[cappedScrollIndex].getBoundingClientRect().y
+      if (Math.abs(err) > virtualScrollIndexY) {
+        approxIndex = cappedScrollIndex
         err = virtualScrollIndexY
       }
 
@@ -210,7 +208,7 @@ const Timeline = {
     handleScroll: throttle(function (e) {
       this.determineVisibleStatuses()
       this.scrollLoad(e)
-    }, 100),
+    }, 150),
     handleVisibilityChange () {
       this.unfocused = document.hidden
     }