let arr = [1,2,3,4]
let arr1 = arr.reverse()
console.log(arr1);  //[4, 3, 2, 1]

let arr2 = [1,2,3,4]
let arr3 = []
arr2.forEach((element) => { 
       arr3.unshift(element)
    })
console.log(arr3);  //[4, 3, 2, 1]

let arr4 = ["jin", "shi","peng"]
let arr5 = []
for (let i = arr4.length-1; i >=0; i--) {
    arr5.push(arr4[i])
}
console.log(arr5);  //['peng', 'shi', 'jin']

動(dòng)態(tài)規(guī)劃法：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);

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)