add support for index

README.md

@@ -38,7 +38,7 @@ forEach(obj, console.log.bind(console))
 // logs out all the values
 ```
 
-Each callback has a method signature of `(value, key, object)` with the exception of `reduce`, which has `(accumulator, value, key, object)`.
+Each callback has a method signature of `(value, key, index, object)` with the exception of `reduce`, which has `(accumulator, value, key, index, object)`. `value` is the current key's value, `key` is the current key's name, `index` is the 0-based index of the current key and `object` is the original object.
 
 **Note:** Unlike the native array equivalent as well as other library implementations, we felt it would be better to explicitly require the passing of an accumulator to the `reduce` method.
 

index.js

@@ -3,27 +3,29 @@
 /**
  * Iterates over an object's keys, applying a transform function to each value.
  * @param  {Object}   obj       - the initial object
- * @param  {Function} transform - the transform function. Receives `(value, key, object)` as arguments.
+ * @param  {Function} transform - the transform function. Receives `(value, key, index, object)` as arguments.
  * @return {Object}             - the new object
  */
 exports.map = function map (obj, transform) {
   let res = {}
+  let index = 0
   for (let [val, key] of entries(obj)) {
-    res[key] = transform(val, key, obj)
+    res[key] = transform(val, key, index++, obj)
   }
   return res
 }
 
 /**
  * Iterates over an object's keys, applying a predicate function that determines whether the current key will appear in the returned object.
  * @param  {Object}   obj       - the initial object
- * @param  {Function} predicate - the predicate function. Receives `(value, key, object)` as arguments. Should return `true` or `false`.
+ * @param  {Function} predicate - the predicate function. Receives `(value, key, index, object)` as arguments. Should return `true` or `false`.
  * @return {Object}             - the new object
  */
 exports.filter = function filter (obj, predicate) {
   let res = {}
+  let index = 0
   for (let [val, key] of entries(obj)) {
-    if (predicate(val, key, obj)) {
+    if (predicate(val, key, index++, obj)) {
       res[key] = val
     }
   }
@@ -33,24 +35,26 @@ exports.filter = function filter (obj, predicate) {
 /**
  * Iterates over an object's keys, calling an iterator function on each pass.
  * @param  {Object}   obj     - the initial object
- * @param  {Function} iterate - the iterator function. Recives `(value, key, object)` as arguments.
+ * @param  {Function} iterate - the iterator function. Recives `(value, key, index, object)` as arguments.
  */
 exports.forEach = function forEach (obj, iterate) {
+  let index = 0
   for (let [val, key] of entries(obj)) {
-    iterate(val, key, obj)
+    iterate(val, key, index++, obj)
   }
 }
 
 /**
  * Iterates over an object's keys, applying a reducer function on each pass that reduces the current parameters into a single value.
  * @param  {Object}   obj         - the initial object.
- * @param  {Function} reducer     - the reducer function. Receives `(accumulator, value, key, object)` as arguments.
+ * @param  {Function} reducer     - the reducer function. Receives `(accumulator, value, key, index, object)` as arguments.
  * @param  {*}        accumulator - a value to accumulate results into.
  * @return {*}                    - the combined accumulated value.
  */
 exports.reduce = function reduce (obj, reducer, accumulator) {
+  let index = 0
   for (let [val, key] of entries(obj)) {
-    accumulator = reducer(accumulator, val, key, obj)
+    accumulator = reducer(accumulator, val, key, index++, obj)
   }
   return accumulator
 }

test/index.js

@@ -1,3 +1,5 @@
+'use strict'
+
 const test = require('ava')
 const {map, reduce, filter, forEach} = require('..')
 const obj = { foo: 'bar', doge: 'wow' }