Add javascript contains duplicate solution

Author: sudheerj

src/javascript/algorithms/array/containsDuplicate.js

@@ -0,0 +1,25 @@
+// TC: O(n), SC: O(1)
+function containsDuplicate(nums) {
+    let noDupsSet = new Set();
+    for(const num of nums) {
+        if(noDupsSet.has(num)) {
+            return true;
+        }
+        noDupsSet.add(num);
+    }
+    return false;
+}
+
+//Use Set size
+function containsDuplicateUsingSize(nums) {
+    return new Set(nums).size !== nums.length;
+}
+
+console.log("-----Has duplicates----");
+let nums1 = [8, 6, 4, 2, 6];
+console.log(containsDuplicate(nums1));
+console.log(containsDuplicateUsingSize(nums1));
+console.log("-----No duplicates----");
+let nums2 = [1, 3, 5, 7, 9];
+console.log(containsDuplicate(nums2));
+console.log(containsDuplicateUsingSize(nums2));