run tdd, update test cases for flatten.

snippets/flatten.md

@@ -16,4 +16,5 @@ const flatten = (arr, depth = 1) =>
 
 ```js
 flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
+flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]
 ```

test/flatten/flatten.js

@@ -1 +1,4 @@
-module.exports = flatten = arr => [].concat(...arr);
+module.exports = flatten = (arr, depth = 1) =>
+depth != 1
+? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flatten(v, depth - 1) : v), [])
+: arr.reduce((a, v) => a.concat(v), []);

test/flatten/flatten.test.js

@@ -6,6 +6,7 @@ test('Testing flatten', (t) => {
 	//Please go to https://github.com/substack/tape
 	t.true(typeof flatten === 'function', 'flatten is a Function');
 	t.deepEqual(flatten([1, [2], 3, 4]), [1, 2, 3, 4], "Flattens an array");
+	t.deepEqual(flatten([1, [2, [3, [4, 5], 6], 7], 8], 2), [1, 2, 3, [4, 5], 6, 7, 8], "Flattens an array");
 	//t.deepEqual(flatten(args..), 'Expected');
 	//t.equal(flatten(args..), 'Expected');
 	//t.false(flatten(args..), 'Expected');