add option to remove extraneous values

Author: nimaen

src/ClassTransformOptions.ts

@@ -26,6 +26,11 @@ export interface ClassTransformOptions {
      */
     strategy?: "excludeAll"|"exposeAll";
 
+    /**
+     * Indicates if extraneous properties should be excluded from the value when converting a plain value to a class.
+     */
+    excludeExtraneousValues?: boolean;
+
     /**
      * Only properties with given groups gonna be transformed.
      */

src/TransformOperationExecutor.ts

@@ -331,7 +331,11 @@ export class TransformOperationExecutor {
                     return key;
                 });
             }
-            keys = keys.concat(exposedProperties);
+            if (this.options.excludeExtraneousValues) {
+                keys = exposedProperties;
+            } else {
+                keys = keys.concat(exposedProperties);
+            }
 
             // exclude excluded properties
             const excludedProperties = defaultMetadataStorage.getExcludedProperties(target, this.transformationType);

test/functional/basic-functionality.spec.ts

@@ -94,6 +94,31 @@ describe("basic functionality", () => {
         });
     });
 
+    it("should exclude extraneous values if the excludeExtraneousValues option is set to true", () => {
+        defaultMetadataStorage.clear();
+
+        class User {
+            @Expose() id: number;
+            @Expose() firstName: string;
+            @Expose() lastName: string;
+        }
+
+        const fromPlainUser = {
+            firstName: "Umed",
+            lastName: "Khudoiberdiev",
+            age: 12
+        };
+
+        const transformedUser = plainToClass(User, fromPlainUser);
+        transformedUser.should.be.instanceOf(User);
+        transformedUser.should.have.property("age");
+        transformedUser.should.have.property("id").that.is.undefined;
+
+        const transformedUserWithoutExtra = plainToClass(User, fromPlainUser, { excludeExtraneousValues: true });
+        transformedUserWithoutExtra.should.be.instanceOf(User);
+        transformedUserWithoutExtra.should.not.have.property("age");
+    });
+
     it("should exclude all objects marked with @Exclude() decorator", () => {
         defaultMetadataStorage.clear();