bugfix(ArrayObserver): ractivejs#3343 - set this of callback using ra…

…ctive

src/Ractive/prototype/observe/Array.ts

@@ -53,7 +53,7 @@ export default class ArrayObserver {
 
   dispatch(): void {
     try {
-      this.callback(this.pending);
+      this.callback.call(this.ractive, this.pending);
     } catch (err) {
       warnIfDebug(
         `Failed to execute array observer callback for '${this.keypath}': ${err.message || err}`

tests/browser/methods/observe.js

@@ -1805,6 +1805,29 @@ export default function() {
     r.push('list', 1);
   });
 
+  test('array observers callback must have ractive instance as this (#3343)', t => {
+    t.expect(2);
+    let thisInsideObserveInitProperty;
+
+    const r = new Ractive({
+      data: { list: [] },
+      observe: {
+        list: {
+          handler() {
+            thisInsideObserveInitProperty = this;
+          },
+          array: true
+        }
+      }
+    });
+
+    r.observe('list', function() {
+      t.equal(this, r);
+    });
+
+    t.equal(r, thisInsideObserveInitProperty);
+  });
+
   test(`plain observers allow a hook to set the 'old' value`, t => {
     t.expect(4);