Javascript prectical questions

Sort an array

function sortArrays(arr)
{
    for (let j = 0; j < length - 1; j++) {
       if (arr[j] > arr[j + 1]) {
          let temp = arr[j];
          arr[j] = arr[j + 1];
          arr[j + 1] = temp;
          j = -1;
        }
     }
    return arr;
}

// Declaring main method
let arr=[1, 2, 99, 9, 8, 7, 6, 0, 5, 4, 3];
arr = sortArrays(arr);

Find Duplicate from array

let array = [6, 9, 15, 6, 13, 9, 11, 15];
      let index = 0, newArr = [];
      const length = array.length; // to get length of array
      function findDuplicates(arr) {
         for (let i = 0; i < length - 1; i++) {
            for (let j = i + 1; j < length; j++) {
            if (arr[i] === arr[j]) {
                  newArr[index] = arr[i];
                  index++;
               }
            }
         }
         return newArr;
      }
let sorted_arr = findDuplicates(array);
console.log(sorted_arr);