properly support iterators in sliced-to-array helper...

src/babel/transformation/templates/sliced-to-array.js

@@ -2,10 +2,35 @@
   if (Array.isArray(arr)) {
     return arr;
   } else if (Symbol.iterator in Object(arr)) {
+    // this is an expanded form of `for...of` that properly supports abrupt completions of
+    // iterators etc. variable names have been minimised to reduce the size of this massive
+    // helper. sometimes spec compliancy is annoying :()
+    //
+    // _n = _iteratorNormalCompletion
+    // _d = _didIteratorError
+    // _e = _iteratorError
+    // _i = _iterator
+    // _s = _step
+
     var _arr = [];
-    for (var val of arr) {
-      _arr.push(_step.value);
-      if (i && _arr.length === i) break;
+    var _n = true;
+    var _d = false;
+    var _e = undefined;
+    try {
+      for (var _i = arr[Symbol.iterator](), _s; !(_n (_s = _i.next()).done); _n = true) {
+        var val = _s.value;
+        _arr.push(_step.value);
+        if (i && _arr.length === i) break;
+      }
+    } catch (err) {
+      _d = true;
+      _e = err;
+    } finally {
+      try {
+        if (!_n && _i["return"]) _i["return"]();
+      } finally {
+        if (_d) throw _e;
+      }
     }
     return _arr;
   } else {