feat(sum): add sum to add all elements in array (#68)

* add sum to add all elements in array

* feat(sum): Add a sum function

Author: Igor Irianto

src/index.js

@@ -18,6 +18,7 @@ import subtract from './subtract'
 import divide from './divide'
 import multiply from './multiply'
 import square from './square'
+import sum from './sum'
 
 export {
   flatten,
@@ -40,4 +41,5 @@ export {
   divide,
   multiply,
   square,
+  sum,
 }

src/pad-left.js

@@ -18,4 +18,3 @@ function padLeft(str, size, padWith) {
     return Array(size - str.length + 1).join(padWith || '0') + str
   }
 }
-

src/sum.js

@@ -0,0 +1,16 @@
+export default sum
+
+/**
+* Original Source: http://stackoverflow.com/questions/1230233/how-to-find-the-sum-of-an-array-of-numbers
+*
+* This method will sum up all the array elements, assuming the elements are all numbers
+*
+* @param {Array} arr - the arr to be summed up
+*
+*/
+
+function sum(arr) {
+  return arr.reduce((a, b) => {
+    return a + b
+  }, 0)
+}

test/pad-left.test.js

@@ -25,4 +25,3 @@ test('does not pad a string longer than the pad length', t => {
   const actual = padLeft(original, padLength)
   t.deepEqual(actual, expected)
 })
-

test/sum.test.js

@@ -0,0 +1,9 @@
+import test from 'ava'
+import {sum} from '../src'
+
+test('sums all array elements', t => {
+  const array = [1,2,3,4,5]
+  const expected = 1 + 2 + 3 + 4 + 5
+  const actual = sum(array)
+  t.deepEqual(actual, expected)
+})