diff --git a/jungmyunggi/2.js b/jungmyunggi/2.js
new file mode 100644
index 0000000..1975723
--- /dev/null
+++ b/jungmyunggi/2.js
@@ -0,0 +1,26 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var lengthOfLongestSubstring = function (s) {
+    let left = 0;
+    let right = 0;
+    const set = new Set();
+    let result = 0;
+    while (right < s.length) {
+        const char = s[right];
+        if (set.has(char)) {
+            while (s[left] !== char) {
+                set.delete(s[left]);
+                left++;
+            }
+            set.delete(s[left]);
+            left++;
+        }
+        set.add(char);
+        result = Math.max(result, right - left + 1);
+        right++;
+    }
+
+    return result;
+};