diff --git a/javascript/0187-repeated-dna-sequences.js b/javascript/0187-repeated-dna-sequences.js
index d126e70d1..66a0a4b01 100644
--- a/javascript/0187-repeated-dna-sequences.js
+++ b/javascript/0187-repeated-dna-sequences.js
@@ -1,8 +1,42 @@
 /**
+ * https://leetcode.com/problems/repeated-dna-sequences/
+ * Hashing
+ * s = the number of letters in the sequence. In our case, it's 10. so the time complexity would be 10*n which boils down to n.
+ * Time O(n) | Space O(n)
  * @param {string} s
  * @return {string[]}
  */
 var findRepeatedDnaSequences = function (s) {
+    const sequenceSet = new Set();
+    let resultSet = new Set();
+
+    for (let i = 0; i < s.length; i++) {
+        const subSequence = getSubSequence(s, i, 10);
+        if (sequenceSet.has(subSequence)) {
+            resultSet.add(subSequence);
+        } else {
+            sequenceSet.add(subSequence);
+        }
+    }
+
+    resultSet = [...resultSet];
+    return resultSet;
+};
+
+function getSubSequence(s, i, len) {
+    return s.slice(i, i + len);
+}
+
+// an alternative code with the same approach.
+/**
+ * https://leetcode.com/problems/repeated-dna-sequences/
+ * Hashing
+ * s = the number of letters in the sequence. In our case, it's 10. so the time complexity would be 10*n which boils down to n.
+ * Time O(n) | Space O(n)
+ * @param {string} s
+ * @return {string[]}
+ */
+var findRepeatedDnaSequences1 = function (s) {
     const seen = new Set();
     const res = new Set();
     const arr = Array.from(s);