JavaScript | with no built-in tools
```\nfunction reverseStr(s: string, k: number): string {\n    const arr = s.split(\'\');\n    \n    for (let i = 0; i < arr.length; i += 2 * k) {\n        let l
```\nfunction reverseStr(s: string, k: number): string {\n    const arr = s.split(\'\');\n    \n    for (let i = 0; i < arr.length; i += 2 * k) {\n        let left = i;\n        let right = i + k - 1;\n        \n        while (left < right) {\n            if (arr[right] === undefined) {\n                right--;\n                continue;\n            }\n            \n            [arr[left], arr[right]] = [arr[right], arr[left]];\n            left++;\n            right--;\n        }\n    }\n    \n    return arr.join(\'\');\n};
['TypeScript', 'JavaScript']