Create firstMissingPositive.js

Author: jv199768

firstMissingPositive.js

@@ -0,0 +1,13 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var firstMissingPositive = function(nums) {
+    const numSet = new Set(nums);
+    let smallest = 1;
+    while(numSet.has(smallest)) {
+        smallest++;
+    }
+    return smallest;
+    
+};