Travis build: 765 [ci skip]

README.md

@@ -272,6 +272,7 @@
 <details>
 <summary>View contents</summary>
 
+* [`join`](#join)
 * [`sortedIndex`](#sortedindex)
 
 </details>
@@ -4589,6 +4590,35 @@ yesNo('Foo', true); // true
 ---
  ## _Uncategorized_
 
+### join
+
+Joins all elements of an array into a string and returns this string. Uses a separator and an end separator.
+
+Use `Array.reduce()` to combine elements into a string.
+Omit the second argument, `separator`, to use a default separator of `','`.
+Omit the third argument, `end`, to use the same value as `separator` by default.
+
+```js
+const join = (arr, separator = ',', end = separator) =>
+  arr.reduce(
+    (acc, val, i) =>
+      i == arr.length - 2
+        ? acc + val + end
+        : i == arr.length - 1 ? acc + val : acc + val + separator,
+    ''
+  );
+```
+
+```js
+join(); // ''
+join(['pen', 'pineapple', 'apple', 'pen'], ',', '&'); //"pen,pineapple,apple&pen"
+join(['pen', 'pineapple', 'apple', 'pen'], ','); //"pen,pineapple,apple,pen"
+join(['pen', 'pineapple', 'apple', 'pen']); //"pen,pineapple,apple,pen"
+```
+
+<br>[⬆ back to top](#table-of-contents)
+
+
 ### sortedIndex
 
 Returns the lowest index at which value should be inserted into array in order to maintain its sort order.