feat(schema): possible now to use ActionSelector without fn callback

Author: emyann

src/MorphismTree.ts

@@ -151,7 +151,6 @@ export class MorphismSchemaTree<Target, Source> {
     queue.push(this.root);
     while (queue.length > 0) {
       let node = queue.shift();
-
       if (node) {
         for (let i = 0, length = node.children.length; i < length; i++) {
           queue.push(node.children[i]);

src/helpers.ts

@@ -15,7 +15,7 @@ import { ActionSelector, ActionAggregator, ActionFunction } from './types';
 export const SCHEMA_OPTIONS_SYMBOL = Symbol('SchemaOptions');
 
 export function isActionSelector<S, R>(value: any): value is ActionSelector<S, R> {
-  return isObject(value) && value.hasOwnProperty('fn') && value.hasOwnProperty('path');
+  return isObject(value) && (value.hasOwnProperty('fn') || value.hasOwnProperty('path'));
 }
 export function isActionString(value: any): value is string {
   return isString(value);

src/morphism.spec.ts

@@ -328,6 +328,17 @@ describe('Morphism', () => {
         let results = Morphism(schema, dataToCrunch);
         expect(results[0]).toEqual(desiredResult);
       });
+      it('should allow to use an action selector without a `fn` specified', () => {
+        interface Source {
+          s1: string;
+        }
+        interface Target {
+          t1: string;
+        }
+        const schema = createSchema<Target, Source>({ t1: { path: 's1' } });
+        const result = morphism(schema, { s1: 'value' });
+        expect(result.t1).toEqual('value');
+      });
     });
     describe('Function Predicate', function() {
       it('should support es6 destructuring as function predicate', function() {