feature(diff): add depth option

index.d.ts

@@ -1,4 +1,8 @@
-export function diff (originalObj: object, updatedObj: object): object
+interface Options {
+  depth: number
+}
+
+export function diff (originalObj: object, updatedObj: object, options: Options): object
 
 export function addedDiff (originalObj: object, updatedObj: object): object
 

src/diff/index.js

@@ -1,26 +1,33 @@
-import { isDate, isEmpty, isObject, properObject } from '../utils';
+import { isDate, isEmpty, isObject, properObject, isNumber } from '../utils';
 
-const diff = (lhs, rhs) => {
+const diff = (lhs, rhs, options = {}) => {
   if (lhs === rhs) return {}; // equal return no diff
 
   if (!isObject(lhs) || !isObject(rhs)) return rhs; // return updated rhs
 
   const l = properObject(lhs);
   const r = properObject(rhs);
 
-  const deletedValues = Object.keys(l).reduce((acc, key) => {
-    return r.hasOwnProperty(key) ? acc : { ...acc, [key]: undefined };
-  }, {});
-
   if (isDate(l) || isDate(r)) {
     if (l.valueOf() == r.valueOf()) return {};
     return r;
   }
 
+  if (isNumber(options.depth)) {
+    if (options.depth === 0) {
+      return r
+    }
+    options.depth -= 1
+  }
+
+  const deletedValues = Object.keys(l).reduce((acc, key) => {
+    return r.hasOwnProperty(key) ? acc : { ...acc, [key]: undefined };
+  }, {});
+
   return Object.keys(r).reduce((acc, key) => {
     if (!l.hasOwnProperty(key)) return { ...acc, [key]: r[key] }; // return added r key
 
-    const difference = diff(l[key], r[key]);
+    const difference = diff(l[key], r[key], options);
 
     if (isObject(difference) && isEmpty(difference) && !isDate(difference)) return acc; // return no diff
 

src/diff/index.test.js

@@ -74,6 +74,10 @@ describe('.diff', () => {
       test('returns keys as undefined when deleted from right hand side', () => {
         expect(diff({ a: 1, b: { c: 2 }}, { a: 1 })).toEqual({ b: undefined });
       });
+
+      test('returns subset of right hand side for first level only', () => {
+        expect(diff({ a: 1, b: { c: 1 } }, { a: 1, b: { d: 2 } }, { depth: 1 })).toEqual({ b: { d: 2 } });
+      });
     });
 
     describe('arrays', () => {

src/utils/index.js

@@ -2,3 +2,4 @@ export const isDate = d => d instanceof Date;
 export const isEmpty = o => Object.keys(o).length === 0;
 export const isObject = o => o != null && typeof o === 'object';
 export const properObject = o => isObject(o) && !o.hasOwnProperty ? { ...o } : o;
+export const isNumber = o => Number(o) !== isNaN(o)