Add JS for chapter of computational complexity

docs/chapter_computational_complexity/space_time_tradeoff.md

@@ -90,7 +90,17 @@ comments: true
 === "JavaScript"
 
     ```js title="leetcode_two_sum.js"
-
+    function twoSumBruteForce(nums, target) {
+      let n = nums.length;
+      // 两层循环，时间复杂度 O(n^2)
+      for (let i = 0; i < n; i++) {
+        for (let j = i + 1; j < n; j++) {
+          if (nums[i] + nums[j] === target) {
+            return [i, j]
+          }
+        }
+      }
+    }
     ```
 
 === "TypeScript"
@@ -193,7 +203,18 @@ comments: true
 === "JavaScript"
 
     ```js title="leetcode_two_sum.js"
-
+    function twoSumHashTable(nums, target) {
+      // 辅助哈希表，空间复杂度 O(n)
+      let m = {}
+      // 单层循环，时间复杂度 O(n)
+      for (let i = 0; i < nums.length; i++) {
+        if (m[nums[i]] !== undefined) {
+          return [m[nums[i]], i]
+        } else {
+          m[target - nums[i]] = i;
+        }
+      }
+    }
     ```
 
 === "TypeScript"