Added find first duplicate and even digits only

Javascript/evenDigitsOnly.js

@@ -0,0 +1,17 @@
+//Check if all the digits of given integer are even
+/* 
+example:
+input :24862
+output:true
+input:642386
+output:false
+*/
+
+function evenDigitsOnly(number) {
+  const digits = number.toString().split("");
+
+  return digits.every((digit) => parseInt(digit % 2) === 0);
+}
+
+const nums = 248632;
+evenDigitsOnly(nums);

Javascript/firstDuplicate.js

@@ -0,0 +1,31 @@
+/*
+Problem:First duplicate number for which the second occurrence
+has smaller index than second occurence of other number does,
+if no such element does return -1
+
+Input:array
+outpur:if duplicate number found return number else return -1
+examples:
+input:[2,1,3,5,3,2]
+result:3
+input:[2,3,4,5,1]
+result:-1
+*/
+
+function firstDuplicate(nums) {
+  const firstDup = {};
+  //iterate the nums
+  for (let num of nums) {
+    //check for duplicate values
+    if (firstDup.hasOwnProperty(num)) {
+      //return duplicated num
+      return num;
+    }
+    firstDup[num] = num;
+  }
+  //dont find return -1
+  return -1;
+}
+
+const nums = [2, 1, 3, 5, 3, 2];
+firstDuplicate(nums);