js实现数组中的一部分反转

动态规划法：
const arr = [2, 6, 5, 8, 3, 5, 2, 6, 7];
const start = 3, end = 7;
const reverse = arr => {
   const { length: l } = arr;
   for(let i = 0; i < Math.floor(l/2); i++){
      const temp = arr[i];
      arr[i] = arr[l-i-1];
      arr[l-i-1] = temp;
   };
   return arr;
};
const reverseBetween = (arr, start, end) => {
   const num = Math.min(end - start, arr.length - start);
   arr.splice(start, 0, ...reverse(arr.splice(start, num)));
}
reverseBetween(arr, start, end);
console.log(arr);

 完全用数组的方法实现

const arr = [1,2,3,4,5,6,7,8]  // 2,5  得 [1,2,6,5,4,3,7,8]
function Fselve(str,a,b){
  let arrary= [];
  let abs = arr.slice(a,b+1).reverse()

  for(var i=0;i<str.length;i++){
    if(i<a){
      arrary.push(str[i])
    }else if(b<i){
      arrary.push(str[i])
    }
  }
  arrary.splice(a,0,abs)
  let newArr =[]
  for(var j=0;j<arrary.length;j++){
    if(arrary[j].length>0){
      for(var h=0;h<arrary[j].length;h++){
        newArr.push(arrary[j][h])
      }
    }else{
      newArr.push(arrary[j])
    }
  }
  console.log(newArr,'new')
  return newArr

}
Fselve(arr,2,5)