add js solution for 001

Author: limbowandering

solution/001.Two Sum/Solution.js

@@ -0,0 +1,11 @@
+const twoSum = function(nums, target) {
+  const map = {};
+
+  for (let i = 0; i < nums.length; i++) {
+    if (map[nums[i]] !== undefined) {
+      return [map[nums[i]], i]
+    } else {
+      map[target - nums[i]] = i
+    }
+  }  
+};