[剑指Offer58-II.左旋转字符串] 添加js版本代码

problems/剑指Offer58-II.左旋转字符串.md

@@ -165,6 +165,37 @@ func reverse(b []byte, left, right int){
 ```
 
 
+javaScript:
+
+```js
+/**
+ * @param {string} s
+ * @param {number} n
+ * @return {string}
+ */
+ var reverseLeftWords = function(s, n) {
+  const strArr = Array.from(s);
+  reverse(strArr, 0, n - 1);
+  reverse(strArr, n, strArr.length - 1);
+  reverse(strArr, 0, strArr.length - 1);
+  return strArr.join('');
+};
+
+// 翻转从 start 到 end 的字符
+function reverse(strArr, start, end) {
+  let left = start;
+  let right = end;
+
+  while(left < right) {
+    // 交换
+    [strArr[left], strArr[right]] = [strArr[right], strArr[left]];
+    left++;
+    right--;
+  }
+}
+```
+
+