diff --git a/component.json b/component.json
index 8629e43..a21c662 100644
--- a/component.json
+++ b/component.json
@@ -2,10 +2,14 @@
   "name": "sum",
   "repo": "component/sum",
   "description": "Array sum utility",
-  "version": "0.1.1",
-  "keywords": ["array", "sum", "utility"],
+  "version": "0.2.0",
+  "keywords": [
+    "array",
+    "sum",
+    "utility"
+  ],
   "dependencies": {
-    "component/to-function": "*"
+    "component/to-function": "1.2.0"
   },
   "development": {},
   "scripts": [
diff --git a/index.js b/index.js
index cad39e3..91e471e 100644
--- a/index.js
+++ b/index.js
@@ -16,11 +16,13 @@ var toFunction = require('to-function');
 
 module.exports = function(arr, fn){
   var sum = 0;
+  var len = arr.length
   if (fn) {
-    fn = toFunction(fn);
-    if (Array.isArray(arr)) {
-      for (var i = 0; i < arr.length; ++i) {
-        sum += fn(arr[i], i);
+    if (typeof fn != 'function') fn = toFunction(fn);
+    // array
+    if (len === +len) {
+      for (var key = 0; key < len; ++key) {
+        sum += fn(arr[key], key);
       }
     } else {
       for (var key in arr) {
@@ -28,8 +30,15 @@ module.exports = function(arr, fn){
       }
     }
   } else {
-    for (var i = 0; i < arr.length; ++i) {
-      sum += arr[i];
+    // array
+    if (len === +len) {
+      for (var key = 0; key < len; ++key) {
+        sum += arr[key]
+      }
+    } else {
+      for (var key in arr) {
+        sum += arr[key]
+      }
     }
   }
   return sum;
diff --git a/package.json b/package.json
index b167640..ec55a1c 100644
--- a/package.json
+++ b/package.json
@@ -1,9 +1,9 @@
 {
   "name": "sum-component",
-  "version": "0.1.1",
+  "version": "0.2.0",
   "description": "Sum utility",
   "dependencies": {
-    "to-function": "*"
+    "to-function": "~1.2.0"
   },
   "devDependencies": {
     "mocha": "*",
diff --git a/test/index.js b/test/index.js
index 84e9de9..195d6e8 100644
--- a/test/index.js
+++ b/test/index.js
@@ -26,10 +26,25 @@ describe('sum(arr)', function(){
       return user.age;
     }).should.equal(11);
   })
+
+  it('should sum array like objects', function(){
+    sum({0:1,1:2,2:3,length:3}).should.equal(6);
+    sum({0:1,1:2,2:3,length:3}, function(item){
+      return item
+    }).should.equal(6);
+  })
 })
 
-describe('sum(obj, fn)', function(){
+describe('sum(obj)', function(){
   it('should sum values', function(){
+    sum({
+      foo: 1,
+      bar: 2,
+      baz: 3
+    }).should.equal(6);
+  })
+
+  it('should support callbacks', function(){
     sum({
       foo: 1,
       bar: 2,