Support a more complex form of enum definition

Author: kourge

__tests__/test.ts

@@ -8,4 +8,11 @@ describe("Enum", () => {
     it("returns an object with values equal to keys given a single string", () => {
         expect(Enum("BLACK")).toEqual({ BLACK: "BLACK" });
     });
+
+    it("returns the original object given an object", () => {
+        expect(Enum({
+            BLACK: "black",
+            WHITE: "white",
+        })).toEqual({ BLACK: "black", WHITE: "white" });
+    });
 });

src/index.ts

@@ -1,7 +1,18 @@
-export function Enum<V extends string>(...values: V[]): { [K in V]: K } {
-    const result: any = {};
-    values.forEach((value) => result[value] = value);
-    return result;
+export function Enum<V extends string>(...values: V[]): { [K in V]: K };
+export function Enum<
+    T extends { [_: string]: V },
+    V extends string
+>(definition: T): T;
+export function Enum(...values: any[]): any {
+    if (typeof values[0] === "string") {
+        const result: any = {};
+        for (const value of values) {
+            result[value] = value;
+        }
+        return result;
+    } else {
+        return values[0];
+    }
 }
 
 export type Enum<T> = T[keyof T];