feat(getMiddle): add getMiddle function (#189)

My first pull request! Had to use --no-verify because some error didn't let me commit the changes though. Thanks again for the opportunity!

Author: d-ivashchuk

Diff for: package.json

@@ -101,4 +101,4 @@
       "kentcdodds/ava"
     ]
   }
-}
+}

Diff for: src/getMiddle.js

@@ -0,0 +1,12 @@
+export default getMiddle
+
+/**
+ * This method will return the character that stays in the middle of the string.
+ *
+ * @param {String} string - string to get the middle character from
+ * @return {String} - middle character of the string
+ **/
+
+function getMiddle(string) {
+  return string.substr(Math.ceil(string.length / 2 - 1), string.length % 2 === 0 ? 2 : 1)
+}

Diff for: src/index.js

@@ -68,6 +68,7 @@ import makeObjectIterable from './makeObjectIterable'
 import fibonacciSum from './fibonacciSum'
 import lcm from './lcm'
 import occurrences from './occurrences'
+import getMiddle from './getMiddle'
 
 export {
   reverseArrayInPlace,
@@ -140,4 +141,5 @@ export {
   fibonacciSum,
   lcm,
   occurrences,
+  getMiddle,
 }

Diff for: test/getMiddle.test.js

@@ -0,0 +1,15 @@
+import test from 'ava'
+import { getMiddle } from '../src'
+
+test('Gets middle character of given string with a length of uneven number of characters ', t => {
+  const string = 'rumpelstiltskin'
+  const expected = 't'
+  const actual = getMiddle(string)
+  t.deepEqual(actual, expected)
+})
+test('Gets  two middle characters of given string with a length of even number of characters ', t => {
+  const string = 'pull'
+  const expected = 'ul'
+  const actual = getMiddle(string)
+  t.deepEqual(actual, expected)
+})