feat(Modules): Add reduce and filter

Use native if present

__tests__/modules/filter.test.js

@@ -0,0 +1,29 @@
+import filter from '../../modules/filter'
+
+describe('filter', () => {
+  test('calls the iterator filter if present', () => {
+    const iterator = {
+      filter: jest.fn()
+    }
+
+    const fn = () => {}
+    filter(fn, iterator)
+
+    expect(iterator.filter).toHaveBeenCalled()
+  })
+
+  test('imitates the array.filter on objects', () => {
+    const obj = {
+      a: 1,
+      b: 2,
+      c: 4
+    }
+
+    const fn = n => n % 2 === 0
+    const result = filter(fn, obj)
+
+    expect(result).toEqual({
+      b: 2, c: 4
+    })
+  })
+})

__tests__/modules/reduce.test.js

@@ -0,0 +1,30 @@
+import reduce from '../../modules/reduce'
+
+describe('identity', () => {
+  test('calls reduce method if located', () => {
+    const it = {
+      reduce: jest.fn()
+    }
+
+    const fn = () => {}
+    const start = {}
+
+    reduce(fn, start, it)
+
+    expect(it.reduce).toHaveBeenCalled()
+  })
+
+  test('mirrors array reduce with objects', () => {
+    const obj = {
+      a: 1,
+      b: 2,
+      c: 3
+    }
+
+    const fn = (acc, curr) => [...acc, curr * 2]
+    const start = []
+    const result = reduce(fn, start, obj)
+
+    expect(result).toEqual([2, 4, 6])
+  })
+})

modules/filter.js

@@ -0,0 +1,21 @@
+import curry from './curry'
+import prop from './prop'
+
+const filter = (fn, iterator) => {
+  if ('filter' in iterator) {
+    return iterator.filter(fn)
+  }
+
+  const result = {}
+
+  for (let key in iterator) {
+    const value = prop(key, iterator)
+    if (fn(value)) {
+      result[key] = value
+    }
+  }
+
+  return result
+}
+
+export default curry(filter)

modules/map.js

@@ -1,16 +1,14 @@
 import curry from './curry'
 
-const mapArray = (fn, list) => list.map(fn)
-
-const map = (fn, list) => {
-  if (Array.isArray(list)) {
-    return mapArray(fn, list)
+const map = (fn, iterator) => {
+  if ('map' in iterator) {
+    return iterator.map(fn)
   }
 
   const result = {}
 
-  for(let k in list) {
-    result[k] = fn(list[k])
+  for(let k in iterator) {
+    result[k] = fn(iterator[k])
   }
 
   return result

modules/reduce.js

@@ -0,0 +1,18 @@
+import curry from './curry'
+import prop from './prop'
+
+const reduce = (fn, start, iterator) => {
+  if ('reduce' in iterator) {
+    return iterator.reduce(fn, start)
+  }
+
+  let result = start
+
+  for(let k in iterator) {
+    result = fn(result, prop(k, iterator))
+  }
+
+  return result
+}
+
+export default curry(reduce)