retain non int array keys

Author: kolodny

index.js

@@ -19,7 +19,7 @@ var getAllKeys = typeof Object.getOwnPropertySymbols === 'function' ?
 /* istanbul ignore next */
 function copy(object) {
   if (object instanceof Array) {
-    return object.slice();
+    return assign(object.constructor(object.length), object)
   } else if (object && typeof object === 'object') {
     var prototype = object.constructor && object.constructor.prototype
     return assign(Object.create(prototype || null), object);

package.json

@@ -1,6 +1,6 @@
 {
   "name": "immutability-helper",
-  "version": "2.2.3",
+  "version": "2.3.0",
   "description": "mutate a copy of data without changing the original source",
   "main": "index.js",
   "scripts": {

test.js

@@ -412,6 +412,16 @@ describe('update', function() {
     expect(a).toBe(b)
     expect(a).toBe(c)
     expect(a).toBe(d)
-  })
+  });
+
+  it('does not lose non integer keys of an array', function() {
+    var state = a = { items: [
+      { name: 'Superman', strength: 1000 },
+      { name: 'Jim', strength: 2 },
+    ] };
+    state.items.top = 0
+    var state2 = update(state, { items: { 1: { strength: { $set: 3 } } } });
+    expect(state2.items.top).toBe(0)
+  });
 
 });