Add solution in JS

Author: udilbar

README.md

@@ -24,3 +24,22 @@ Because `nums[0] + nums[1] == 9`, we return `[0, 1]`.
 
 **Only one valid answer exists.**
 
+## Solution in JavaScript:
+
+```
+var twoSum = function(nums, target) {
+    let targetFirstIndex, targetLastIndex;
+    
+    for (let i = 0; i < nums.length; i++) {
+        for (let j = i + 1; j < nums.length; j++) {
+            if (nums[i] + nums[j] === target) {
+                targetFirstIndex = i;
+                targetLastIndex = j;
+                break;
+            } 
+        }
+    }
+    
+    return [targetFirstIndex, targetLastIndex];
+};
+```