add functional auto-curried syntax support

README.md

@@ -2,23 +2,31 @@
 
 [![npm](http://img.shields.io/npm/v/objectfn.svg?style=flat)](https://badge.fury.io/js/objectfn) [![tests](http://img.shields.io/travis/jescalan/objectfn/master.svg?style=flat)](https://travis-ci.org/jescalan/objectfn) [![dependencies](http://img.shields.io/david/jescalan/objectfn.svg?style=flat)](https://david-dm.org/jescalan/objectfn) [![coverage](http://img.shields.io/coveralls/jescalan/objectfn.svg?style=flat)](https://coveralls.io/github/jescalan/objectfn)
 
-Map, reduce, forEach, and filter for objects. Lazy evaluation, no dependencies.
+`map`, `reduce`, `forEach`, and `filter` for plain objects. Lazy evaluation, supports functional & imperative syntax, no dependencies.
 
 ### Why should you care?
 
 I wanted a library that has no dependencies and gives me the basic map/reduce/filter for use on objects. Any existing library I found has boatloads of dependencies, provides tons more extra tools, and/or is unmaintained. So here's `ObjectFn`, just for you!
 
 Also, big props to [@declandewet](https://github.com/declandewet) for the initial implementation of this library!
 
+### Requirements
+
+- [Node.js v.6+](http://nodejs.org)
+
 ### Installation
 
-`npm install objectfn -S`
+Using a terminal:
 
-> **Note:** This project is compatible with node v6+ only
+`npm install objectfn -S`
 
 ### Usage
 
-Very straightforward usage. Just import what you need and use it on an object.
+Usage is straightforward. Just import what you need and use it on an object.
+
+#### Imperative style
+
+Takes data first, callback last.
 
 ```js
 const {map, reduce, filter, forEach} = require('objectfn')
@@ -38,9 +46,39 @@ forEach(obj, console.log.bind(console))
 // logs out all the values
 ```
 
+#### Functional style
+
+Takes callback first, data last. Each method is automatically curried.
+
+```js
+const {map, reduce, filter, forEach} = require('objectfn')
+
+const obj = { foo: 'bar', wow: 'doge' }
+
+const mapper = map((val, key) => val.toUpperCase())
+mapper(obj)
+// { foo: 'BAR', wow: 'DOGE' }
+
+const reducer = reduce((accum, val, key) => accum[val.toUpperCase()] = key && accum }, {})
+reducer(obj)
+// { FOO: 'bar', WOW: 'doge' }
+
+const filterer = filter((val, key) => !key === 'foo')
+filterer(obj)
+// { wow: 'doge' }
+
+const iterator = forEach(console.log.bind(console))
+iterator(obj)
+// logs out all the values
+```
+
+### Method Signature
+
 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.
+### Differences in `reduce`
+
+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.
 
 This means that this will work:
 
@@ -56,6 +94,14 @@ let obj = { one: 1, two: 2, three: 3, four: 4 }
 reduce(obj, (prevVal, currVal) => prevVal + currVal) // => wat?
 ```
 
+### Binding `this`
+
+Unlike native (and a small handful of other third-party) implementations, this library offers no mechanism for binding the `this` context of the callback via the last parameter. If you want this, it is far more readable to do so using `Function.prototype.bind`:
+
+```js
+map(obj, fn.bind(/* value to use as `this` goes here */))
+```
+
 ### License & Contributing
 
 - Details on the license [can be found here](LICENSE.md)

index.js

@@ -1,10 +1,19 @@
+// curry the callWithReorderedArgs function
+const flippable = curry(callWithReorderedArgs)
+
+// export argument-flippable auto-curried methods
+exports.map = flippable(curry(map))
+exports.filter = flippable(curry(filter))
+exports.reduce = flippable(curry(reduce))
+exports.forEach = flippable(curry(forEach))
+
 /**
  * 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, index, object)` as arguments.
+ * @param  {Object}   obj       - the initial object
  * @return {Object}             - the new object
  */
-exports.map = function map (obj, transform) {
+function map (transform, obj) {
   let res = {}
   let index = 0
   for (let [val, key] of entries(obj)) {
@@ -15,11 +24,11 @@ exports.map = function map (obj, transform) {
 
 /**
  * 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, index, object)` as arguments. Should return `true` or `false`.
+ * @param  {Object}   obj       - the initial object
  * @return {Object}             - the new object
  */
-exports.filter = function filter (obj, predicate) {
+function filter (predicate, obj) {
   let res = {}
   let index = 0
   for (let [val, key] of entries(obj)) {
@@ -32,10 +41,10 @@ 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, index, object)` as arguments.
+ * @param  {Object}   obj     - the initial object
  */
-exports.forEach = function forEach (obj, iterate) {
+function forEach (iterate, obj) {
   let index = 0
   for (let [val, key] of entries(obj)) {
     iterate(val, key, index++, obj)
@@ -44,12 +53,12 @@ exports.forEach = function forEach (obj, iterate) {
 
 /**
  * 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, index, object)` as arguments.
  * @param  {*}        accumulator - a value to accumulate results into.
+ * @param  {Object}   obj         - the initial object.
  * @return {*}                    - the combined accumulated value.
  */
-exports.reduce = function reduce (obj, reducer, accumulator) {
+function reduce (reducer, accumulator, obj) {
   let index = 0
   for (let [val, key] of entries(obj)) {
     accumulator = reducer(accumulator, val, key, index++, obj)
@@ -67,3 +76,28 @@ function * entries (obj) {
     yield [obj[key], key]
   }
 }
+
+/**
+ * Calls a function with supplied arguments - if first argument (`obj`) is not a function, it is moved to the end of the argument list.
+ * @param  {Function} fn       - a function to call
+ * @param  {*}        firstArg - the first argument
+ * @param  {*}        args...  - the rest of the arguments
+ * @return {*}                 - the result of calling `fn()` with supplied args
+ */
+function callWithReorderedArgs (fn, firstArg, ...args) {
+  return typeof firstArg === 'function'
+    ? fn(firstArg, ...args)
+    : fn(...args, firstArg)
+}
+
+/**
+ * Accepts a function, returning a function that partially-applies itself when there are missing arguments.
+ * @param  {Function} fn - the function to curry
+ * @return {Function}    - the curried function.
+ */
+function curry (fn) {
+  const partial = (...args) => args.length < fn.length
+    ? (...partialArgs) => partial(...args.concat(partialArgs))
+    : fn(...args)
+  return partial
+}

test/curried.js

@@ -0,0 +1,31 @@
+const test = require('ava')
+const {map, reduce, filter, forEach} = require('..')
+const obj = { foo: 'bar', doge: 'wow' }
+
+test('forEach', (t) => {
+  t.plan(2)
+  const fn = forEach((v, k) => t.truthy(obj[k] === v))
+  fn(obj)
+})
+
+test('map', (t) => {
+  const fn = map((v, k) => v.toUpperCase())
+  const mapped = fn(obj)
+  t.truthy(mapped.foo === 'BAR')
+  t.truthy(mapped.doge === 'WOW')
+})
+
+test('filter', (t) => {
+  const fn = filter((v, k) => k !== 'doge')
+  const filtered = fn(obj)
+  t.truthy(filtered.foo === 'bar')
+  t.falsy(filtered.doge === 'wow')
+})
+
+test('reduce', (t) => {
+  const fn = reduce((m, v, k) => m.push(v) && m, [])
+  const reduced = fn(obj)
+  t.truthy(reduced.length === 2)
+  t.truthy(reduced[0] === 'bar')
+  t.truthy(reduced[1] === 'wow')
+})

test/functional.js

@@ -0,0 +1,27 @@
+const test = require('ava')
+const {map, reduce, filter, forEach} = require('..')
+const obj = { foo: 'bar', doge: 'wow' }
+
+test('forEach', (t) => {
+  t.plan(2)
+  forEach((v, k) => t.truthy(obj[k] === v), obj)
+})
+
+test('map', (t) => {
+  const mapped = map((v, k) => v.toUpperCase(), obj)
+  t.truthy(mapped.foo === 'BAR')
+  t.truthy(mapped.doge === 'WOW')
+})
+
+test('filter', (t) => {
+  const filtered = filter((v, k) => k !== 'doge', obj)
+  t.truthy(filtered.foo === 'bar')
+  t.falsy(filtered.doge === 'wow')
+})
+
+test('reduce', (t) => {
+  const reduced = reduce((m, v, k) => m.push(v) && m, [], obj)
+  t.truthy(reduced.length === 2)
+  t.truthy(reduced[0] === 'bar')
+  t.truthy(reduced[1] === 'wow')
+})