feat(swapCase): add a swapCase function (#88)

Author: jefferson-silva

src/index.js

@@ -28,6 +28,7 @@ import searchAndReplace from './search-and-replace'
 import sqrt from './sqrt'
 import toPower from './to-power'
 import mod from './mod'
+import swapCase from './swap-case'
 
 export {
   initArray,
@@ -59,4 +60,5 @@ export {
   sqrt,
   toPower,
   mod,
+  swapCase,
 }

src/swap-case.js

@@ -0,0 +1,17 @@
+export default swapCase
+
+/**
+ * Original source: http://stackoverflow.com/a/40192407/4204587
+ *
+ * This method will swap cases for a given string.
+ *
+ * @param {String} s - string for case swapping
+ * @return {String} - string with all cases swapped
+ */
+function swapCase(s) {
+  return s.split('').map(function swapper(c) {
+    return c === c.toUpperCase() ?
+           c.toLowerCase() :
+           c.toUpperCase()
+  }).join('')
+}

test/swap-case.test.js

@@ -0,0 +1,9 @@
+import test from 'ava'
+import {swapCase} from '../src'
+
+test('Swap cases from string ', t => {
+  const original = 'That\'s one small step for a DEVELOPER, one giant leap for a Community.'
+  const expected = 'tHAT\'S ONE SMALL STEP FOR A developer, ONE GIANT LEAP FOR A cOMMUNITY.'
+  const actual = swapCase(original)
+  t.is(actual, expected)
+})