From 92ae098659f2fc81e33efe428069236d2d94eebb Mon Sep 17 00:00:00 2001
From: Aaron Jensen <aaronjensen@gmail.com>
Date: Sun, 9 Aug 2015 00:21:24 -0700
Subject: [PATCH] Make u.map return same instance if nothing changes

---
 CHANGELOG.md     |  1 +
 lib/map.js       | 34 ++++++++++++++++++++++++++++------
 test/map-spec.js | 13 +++++++++++++
 3 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index de485c2..4dc8059 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # Change Log
 
 ## [unreleased]
+* `u.map` will now return the same instance if nothing changes.
 * Removed a couple lodash dependencies.
 
 ## [0.5.0]
diff --git a/lib/map.js b/lib/map.js
index a7eecfe..ecf016b 100644
--- a/lib/map.js
+++ b/lib/map.js
@@ -1,15 +1,37 @@
-import mapValues from 'lodash/object/mapValues';
 import update from './update';
 import wrap from './wrap';
 
-function map(iteratee, object) {
-  const updater = update(iteratee);
-
+function forEach(object, callback) {
   if (Array.isArray(object)) {
-    return object.map(updater);
+    object.forEach(callback);
+  } else {
+    Object.keys(object).forEach((key) => callback(object[key], key));
+  }
+}
+
+function clone(object) {
+  if (Array.isArray(object)) {
+    return [...object];
   }
 
-  return mapValues(object, updater);
+  return { ...object };
+}
+
+function map(iteratee, object) {
+  const updater = update(iteratee);
+  let newObject;
+
+  forEach(object, (value, index) => {
+    const newValue = updater(value, index);
+
+    if (newValue === value) return;
+
+    newObject = newObject || clone(object);
+
+    newObject[index] = newValue;
+  });
+
+  return newObject || object;
 }
 
 export default wrap(map);
diff --git a/test/map-spec.js b/test/map-spec.js
index d20d716..198c00b 100644
--- a/test/map-spec.js
+++ b/test/map-spec.js
@@ -25,6 +25,19 @@ describe('u.map', () => {
     expect(result).to.eql([{ a: 1 }, { a: 1 }]);
   });
 
+  it('returns the same object if no updates are made', () => {
+    const array = [0, 1];
+    const ident = x => x;
+    let result = u.map(ident, array);
+
+    expect(result).to.equal(array);
+
+    const object = { a: 0 };
+    result = u.map(ident, object);
+
+    expect(result).to.equal(object);
+  });
+
   it('passes the key or index as the second parameter to the iteratee', () => {
     const object = {
       a: { x: 0 },