Walk 4 states, concat revertSteps

src/content_script.js

@@ -42,25 +42,28 @@ function hideBanners() {
     })
   })
 
-  const revert = () => revertSteps.forEach(step => step())
-  return revert
+  return revertSteps
 }
 
 
 function main() {
-  let active = false
-  let revert
+  let state = 'off'
+  let revertSteps = []
 
   function onScroll() {
     let action
-    if (window.scrollY > 20 && !active) {
-      active = true
-      action = () => { revert = hideBanners() }
-    } else if (window.scrollY <= 0 && active) {
-      active = false
+    if (window.scrollY > 20 && state === 'off') {
+      state = 'starting'
       action = () => {
-        revert && revert()
-        revert = undefined
+        revertSteps = revertSteps.concat(hideBanners())
+        state = 'on'
+      }
+    } else if (window.scrollY <= 0 && state === 'on') {
+      state = 'stopping'
+      action = () => {
+        revertSteps.forEach(step => step())
+        revertSteps = []
+        state = 'off'
       }
     }
     if (action) {