2 files changed, 15 insertions, 3 deletions
diff --git a/src/extensions/ExtensionsTypings.ts b/src/extensions/ExtensionsTypings.ts
index d6ffd3be3..fa8851bb3 100644
--- a/src/extensions/ExtensionsTypings.ts
+++ b/src/extensions/ExtensionsTypings.ts
@@ -1,6 +1,14 @@
 /* eslint-disable @typescript-eslint/no-unused-vars */
 interface Array<T> {
+    /**
+     * returns the last element of the array or undefined
+     */
     lastElement(): T;
+    /**
+     * if val is in the list, it returns its index, otherwise undefined;
+     * @param val
+     */
+    getIndex(val: T): number | undefined;
 }
 
 interface String {
diff --git a/src/extensions/Extensions_Array.ts b/src/extensions/Extensions_Array.ts
index a50fb330f..d61585e28 100644
--- a/src/extensions/Extensions_Array.ts
+++ b/src/extensions/Extensions_Array.ts
@@ -1,14 +1,13 @@
 export default class ArrayExtension {
     private readonly property: string;
-    private readonly body: <T>(this: Array<T>) => any;
+    private readonly body: <T>(this: Array<T>, args: unknown) => unknown;
 
-    constructor(property: string, body: <T>(this: Array<T>) => any) {
+    constructor(property: string, body: <T>(this: Array<T>, args: unknown) => unknown) {
         this.property = property;
         this.body = body;
     }
 
     assign() {
-        // eslint-disable-next-line no-extend-native
         Object.defineProperty(Array.prototype, this.property, {
             value: this.body,
             enumerable: false,
@@ -28,6 +27,11 @@ const extensions = [
         }
         return this[this.length - 1];
     }),
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    new ArrayExtension('getIndex', function (val: any) {
+        const index = this.indexOf(val);
+        return index === -1 ? undefined : index;
+    }),
 ];
 
 function Assign() {