fixed fatal mobx extension-related error, still can use extensions

1 files changed, 29 insertions, 5 deletions

diff --git a/src/extensions/ArrayExtensions.ts b/src/extensions/ArrayExtensions.ts
index 422a10dbc..8e125766d 100644
--- a/src/extensions/ArrayExtensions.ts
+++ b/src/extensions/ArrayExtensions.ts
@@ -1,13 +1,37 @@
-function Assign() {
+export default class ArrayExtension {
+    private readonly property: string;
+    private readonly body: <T>(this: Array<T>) => any;
+
+    constructor(property: string, body: <T>(this: Array<T>) => any) {
+        this.property = property;
+        this.body = body;
+    }
+
+    assign() {
+        Object.defineProperty(Array.prototype, this.property, {
+            value: this.body,
+            enumerable: false
+        });
+    }
 
-    Array.prototype.lastElement = function <T>() {
+}
+
+/**
+ * IMPORTANT: Any extension you add here *must* have a corresponding type definition
+ * in the Array<T> interface in ./General/ExtensionsTypings.ts. Otherwise,
+ * Typescript will not recognize your new function.
+ */
+const extensions = [
+    new ArrayExtension("lastElement", function () {
         if (!this.length) {
             return undefined;
         }
-        const last: T = this[this.length - 1];
-        return last;
-    };
+        return this[this.length - 1];
+    })
+];
 
+function Assign() {
+    extensions.forEach(extension => extension.assign());
 }
 
 export { Assign };
\ No newline at end of file