diff --git a/src/arrayMethodJoin.js b/src/arrayMethodJoin.js
index 3a62201c..82ce7568 100644
--- a/src/arrayMethodJoin.js
+++ b/src/arrayMethodJoin.js
@@ -4,8 +4,20 @@
  * Implement method join
  */
 function applyCustomJoin() {
-  [].__proto__.join2 = function(separator) {
-    // write code here
+  [].__proto__.join2 = function(separator = ',') {
+    let str = '';
+
+    for (let i = 0; i <= this.length; i++) {
+      if (this[i] !== null && this[i] !== undefined) {
+        str += this[i];
+      }
+
+      if (i < this.length - 1) {
+        str += separator;
+      }
+    }
+
+    return str;
   };
 }