Clean up custom scroll position implementation (#55)

modules/useScrollToTop.js

@@ -1,6 +1,7 @@
 import { POP } from 'history/lib/Actions'
 
 import createUseScroll from './utils/createUseScroll'
+import scrollTo from './utils/scrollTo'
 import setScrollRestoration from './utils/setScrollRestoration'
 
 /**
@@ -11,18 +12,17 @@ import setScrollRestoration from './utils/setScrollRestoration'
 export default function useScrollToTop(createHistory) {
   let unsetScrollRestoration
 
-  function updateScroll({ action }, customPosition) {
-    const [ x, y ] = customPosition || [ 0, 0 ]
+  function getScrollPosition({ action }) {
     // If we didn't manage to disable the default scroll restoration, and it's
     // a pop transition for which the browser might restore scroll position,
     // then let the browser update to its remembered scroll position first,
     // before we set the actual correct scroll position.
     if (action === POP && !unsetScrollRestoration) {
-      setTimeout(() => window.scrollTo(x, y))
-      return
+      setTimeout(() => scrollTo([ 0, 0 ]))
+      return null
     }
 
-    window.scrollTo(x, y)
+    return [ 0, 0 ]
   }
 
   function start() {
@@ -38,5 +38,5 @@ export default function useScrollToTop(createHistory) {
     }
   }
 
-  return createUseScroll(updateScroll, start, stop)(createHistory)
+  return createUseScroll(getScrollPosition, start, stop)(createHistory)
 }

modules/useSimpleScroll.js

@@ -17,14 +17,13 @@ export default function useSimpleScroll(createHistory) {
   // Don't override the browser's scroll behavior here - we actively want the
   // the browser to take care of scrolling on `POP` transitions.
 
-  function updateScroll({ action }, customPosition) {
+  function getScrollPosition({ action }) {
     if (action === POP) {
-      return
+      return null
     }
 
-    const [ x, y ] = customPosition || [ 0, 0 ]
-    window.scrollTo(x, y)
+    return [ 0, 0 ]
   }
 
-  return createUseScroll(updateScroll)(createHistory)
+  return createUseScroll(getScrollPosition)(createHistory)
 }

modules/useStandardScroll.js

@@ -18,8 +18,9 @@ export default function useStandardScroll(createHistory) {
 
   function getScrollPosition() {
     const state = readState(currentKey)
-    if (!state) {
-      return null
+
+    if (!state || !state.scrollPosition) {
+      return [ 0, 0 ]
     }
 
     return state.scrollPosition
@@ -31,11 +32,6 @@ export default function useStandardScroll(createHistory) {
     currentKey = key
   }
 
-  function updateScroll(location, customPosition) {
-    const [ x, y ] = customPosition || getScrollPosition() || [ 0, 0 ]
-    window.scrollTo(x, y)
-  }
-
   let unsetScrollRestoration, unlistenScroll, unlistenBefore
 
   function start(history) {
@@ -92,6 +88,6 @@ export default function useStandardScroll(createHistory) {
   }
 
   return createUseScroll(
-    updateScroll, start, stop, updateLocation
+    getScrollPosition, start, stop, updateLocation
   )(createHistory)
 }

modules/utils/createUseScroll.js

@@ -1,5 +1,7 @@
+import scrollTo from './scrollTo'
+
 export default function createUseScroll(
-  updateScroll, start, stop, updateLocation
+  getScrollPosition, start, stop, updateLocation
 ) {
   return function (createHistory) {
     return function (options = {}) {
@@ -46,11 +48,19 @@ export default function createUseScroll(
           updateLocation(location)
         }
 
-        const updateDecision = shouldUpdateScroll && shouldUpdateScroll(oldLocation, currentLocation)
+        let scrollPosition
+        if (shouldUpdateScroll) {
+          scrollPosition = shouldUpdateScroll(oldLocation, currentLocation)
+        } else {
+          scrollPosition = true
+        }
+
+        if (scrollPosition && !Array.isArray(scrollPosition)) {
+          scrollPosition = getScrollPosition(currentLocation)
+        }
 
-        if (!shouldUpdateScroll || updateDecision) {
-          const customPosition = Array.isArray(updateDecision) ? updateDecision : null
-          updateScroll(location, customPosition)
+        if (scrollPosition) {
+          scrollTo(scrollPosition)
         }
       }
 

modules/utils/scrollTo.js

@@ -0,0 +1,3 @@
+export default function scrollTo([ x, y ]) {
+  window.scrollTo(x, y)
+}