feat(flatten): Implement variable arity for flatten function, add test

src/flatten.js

@@ -3,14 +3,13 @@ export default flatten
 /**
  * Original Source: http://stackoverflow.com/a/15030117/971592
  *
- * This method will flatten an array given to it.
+ * This method will flatten arrays given to it.
  *
- * @param {Array} arr - The array to flatten
+ * @param {...Array} arrays - The array(s) to flatten
  * @return {Array} - The flattened array
  */
-function flatten(arr) {
-  return arr.reduce(function flattenReducer(flat, toFlatten) {
-    return flat.concat(Array.isArray(toFlatten) ? flatten(toFlatten) : toFlatten)
+function flatten() {
+  return [].slice.call(arguments).reduce(function flattenReducer(flat, toFlatten) {
+    return flat.concat(Array.isArray(toFlatten) ? flatten.apply(null, toFlatten) : toFlatten)
   }, [])
 }
-

test/flatten.test.js

@@ -7,3 +7,12 @@ test('flattens an array of arrays', t => {
   const actual = flatten(original)
   t.same(actual, expected)
 })
+
+test('flattens multiple arrays', t => {
+  const original1 = [[1, 2], 3, [4, 5]]
+  const original2 = ['A', 'b', ['C', ['d', 'E']]]
+  const original3 = [true, false, true, false]
+  const expected = [1, 2, 3, 4, 5, 'A', 'b', 'C', 'd', 'E', true, false, true, false]
+  const actual = flatten(original1, original2, original3)
+  t.same(actual, expected)
+})