完成编码挑战-交换数字

I am trying to finalise this coding challenge: https://www.hackerrank.com/challenges/lilys-homework/problem , but am unsure how I should approach the last if statement. Other approaches in solving this are welcome as well.

function lilysHomework(arr) {
    console.log(arr)
    let sortedarr = arr.sort(function(a,b){return a-b})
    console.log(sortedarr)
    for(var i=0;i<arr.length;i++){
      if(arr[i] == sortedarr[i]){
        continue
      } else if(arr[i] !== sortedarr[i]){
        for(var j=0; j<arr.length;j++){
          if(arr[i] == sortedarr.indexOf()){

        }
      }
    }
  }