反转字符串

/**
 * 反转字符串
 */
const reverseString = (str = 'hello world') => {
    const arr = str.split('')
    let startIndex = 0, endIndex = arr.length
    while(startIndex < endIndex) {
        let s = arr[startIndex]
        arr[startIndex] = arr[endIndex]
        arr[endIndex] = s
        startIndex++
        endIndex--
    }
    return arr.join('')
}