fix: always save the initial scroll position even if no scrolling occurs

src/index.js

@@ -102,6 +102,13 @@ export default class ScrollBehavior {
       },
     };
 
+    // In case no scrolling occurs, save the initial position
+    if (!scrollElement.savePositionHandle) {
+      scrollElement.savePositionHandle = requestAnimationFrame(
+        saveElementPosition,
+      );
+    }
+
     this._scrollElements[key] = scrollElement;
     on(element, 'scroll', scrollElement.onScroll);
 
@@ -126,7 +133,15 @@ export default class ScrollBehavior {
   }
 
   updateScroll(prevContext, context) {
-    this._updateWindowScroll(prevContext, context);
+    this._updateWindowScroll(prevContext, context).then(() => {
+      // Save the position immediately after a transition so that if no
+      // scrolling occurs, there is still a saved position
+      if (!this._saveWindowPositionHandle) {
+        this._saveWindowPositionHandle = requestAnimationFrame(
+          this._saveWindowPosition,
+        );
+      }
+    });
 
     Object.keys(this._scrollElements).forEach(key => {
       this._updateElementScroll(key, prevContext, context);
@@ -216,7 +231,7 @@ export default class ScrollBehavior {
     // scroll it isn't enough. Instead, try to scroll a few times until it
     // works.
     this._numWindowScrollAttempts = 0;
-    this._checkWindowScrollPosition();
+    return this._checkWindowScrollPosition();
   }
 
   _updateElementScroll(key, prevContext, context) {
@@ -282,7 +297,7 @@ export default class ScrollBehavior {
     // Still, check anyway just in case.
     /* istanbul ignore if: paranoid guard */
     if (!this._windowScrollTarget) {
-      return;
+      return Promise.resolve();
     }
 
     this.scrollToTarget(window, this._windowScrollTarget);
@@ -291,13 +306,16 @@ export default class ScrollBehavior {
 
     /* istanbul ignore if: paranoid guard */
     if (this._numWindowScrollAttempts >= MAX_SCROLL_ATTEMPTS) {
+      // This might happen if the scroll position was already set to the target
       this._windowScrollTarget = null;
-      return;
+      return Promise.resolve();
     }
 
-    this._checkWindowScrollHandle = requestAnimationFrame(
-      this._checkWindowScrollPosition,
-    );
+    return new Promise(resolve => {
+      this._checkWindowScrollHandle = requestAnimationFrame(() =>
+        resolve(this._checkWindowScrollPosition()),
+      );
+    });
   };
 
   scrollToTarget(element, target) {

test/ScrollBehavior.test.js

@@ -141,6 +141,32 @@ describe('ScrollBehavior', () => {
             },
           ]);
         });
+
+        it('should save position even if it does not change', done => {
+          const history = withRoutes(
+            withScroll(createHistory(), (prevLoc, loc) =>
+              loc.action === 'PUSH' ? [10, 20] : true,
+            ),
+          );
+
+          unlisten = run(history, [
+            () => {
+              history.push('/detail');
+            },
+            () => {
+              history.push('/');
+            },
+            () => {
+              history.push('/detail');
+            },
+            () => history.goBack(),
+            () => {
+              expect(scrollLeft(window)).to.equal(10);
+              expect(scrollTop(window)).to.equal(20);
+              done();
+            },
+          ]);
+        });
       });
 
       describe('scroll element', () => {

test/run.js

@@ -1,6 +1,8 @@
 export function delay(cb) {
   // Give throttled scroll listeners time to settle down.
-  requestAnimationFrame(() => requestAnimationFrame(cb));
+  requestAnimationFrame(() =>
+    requestAnimationFrame(() => requestAnimationFrame(cb)),
+  );
 }
 
 export default function run(history, steps) {