Merge branch 'develop' (closes #105)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "shifty",
-  "version": "2.6.0",
+  "version": "2.6.1",
   "homepage": "http://jeremyckahn.github.io/shifty/doc/",
   "author": "Jeremy Kahn <[email protected]>",
   "repository": {

src/tweenable.js

@@ -193,8 +193,13 @@ const remove = tween => {
     const previousTween = tween._previous;
     const nextTween = tween._next;
 
-    previousTween._next = nextTween;
-    nextTween._previous = previousTween;
+    if (previousTween) {
+      previousTween._next = nextTween;
+    }
+
+    if (nextTween) {
+      nextTween._previous = previousTween;
+    }
   }
 };
 

test/index.js

@@ -394,6 +394,64 @@ describe('shifty', () => {
             'The tweened value jumps to the end'
           );
         });
+
+        describe('repeated calls (#105)', () => {
+          describe('first tween is stopped twice', () => {
+            beforeEach(() => {
+              Tweenable.now = () => 0;
+
+              let { tweenable } = tween({
+                from: { x: 0 },
+                to: { x: 10 },
+                duration: 500,
+              });
+
+              tween({
+                from: { x: 0 },
+                to: { x: 10 },
+                duration: 500,
+              });
+
+              Tweenable.now = () => 250;
+              processTweens();
+
+              tweenable.stop(true);
+              tweenable.stop(true);
+            });
+
+            it('does not break when multiple tweens are running and stop() is called twice', () => {
+              assert(true);
+            });
+          });
+
+          describe('second tween is stopped twice', () => {
+            beforeEach(() => {
+              Tweenable.now = () => 0;
+
+              tween({
+                from: { x: 0 },
+                to: { x: 10 },
+                duration: 500,
+              });
+
+              let { tweenable } = tween({
+                from: { x: 0 },
+                to: { x: 10 },
+                duration: 500,
+              });
+
+              Tweenable.now = () => 250;
+              processTweens();
+
+              tweenable.stop(true);
+              tweenable.stop(true);
+            });
+
+            it('does not break when multiple tweens are running and stop() is called twice', () => {
+              assert(true);
+            });
+          });
+        });
       });
 
       describe('#setScheduleFunction', () => {