stage-1

src/arrayMethodJoin.js

@@ -1,11 +1,62 @@
 'use strict';
 
-/**
- * Implement method join
- */
 function applyCustomJoin() {
+  /**
+   * @param {string | undefined} separator
+   * @returns {string} */
   [].__proto__.join2 = function(separator) {
-    // write code here
+    let inerSeparator;
+    let joined = '';
+    let temp = '';
+
+    if (this.length === 0) {
+      return joined;
+    }
+
+    switch (separator) {
+      case null:
+        inerSeparator = 'null';
+        break;
+
+      case undefined:
+        inerSeparator = ',';
+        break;
+
+      default:
+        inerSeparator = separator;
+    }
+
+    for (let i = 0, last = this.length - 1; ; i++) {
+      temp = this[i];
+
+      switch (temp) {
+        case null:
+        case undefined:
+          temp = '';
+          break;
+        case true:
+          temp = 'true';
+          break;
+        case false:
+          temp = 'false';
+          break;
+        case NaN:
+          temp = 'NaN';
+          break;
+        default:
+          break;
+      }
+
+      joined += temp;
+
+      if (i === last) {
+        break;
+      }
+
+      joined += inerSeparator;
+    }
+
+    return joined;
   };
 }