add polyfill for Object.assign (IE 11 issue)

Author: anna-apanasik

src/index.js

@@ -1,3 +1,4 @@
+import './polyfill'
 import SketchField from './SketchField'
 import Tools from './tools'
 

src/polyfill.js

@@ -0,0 +1,29 @@
+/**
+ * Object.assign() polyfill for IE11
+ * @see <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign>
+ */
+
+if (typeof Object.assign != "function") {
+    Object.defineProperty(Object, "assign", {
+        value: function assign(target, varArgs) {
+            "use strict";
+            if (target == null) {
+                throw new TypeError("Cannot convert undefined or null to object");
+            }
+            var to = Object(target);
+            for (var index = 1; index < arguments.length; index++) {
+                var nextSource = arguments[index];
+                if (nextSource != null) {
+                    for (var nextKey in nextSource) {
+                        if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
+                            to[nextKey] = nextSource[nextKey];
+                        }
+                    }
+                }
+            }
+            return to;
+        },
+        writable: true,
+        configurable: true
+    });
+}