added solution for concatenation of array, p1929

Author: sagnikc395

Diff for: javascript/1929-Concatenation-of-Array.js

@@ -0,0 +1,13 @@
+//https://leetcode.com/problems/concatenation-of-array/description/
+
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+var getConcatenation = function (nums) {
+  let res = [];
+  for (let i = 0; i < nums.length * 2; i++) {
+    res.push(nums[i % nums.length]);
+  }
+  return res;
+};