Both

'use strict';

function filterArray(array) {
  let finalArray = [];

  while (array.length > 0) {
      let biggestNumber = Math.max(...array);
      let smallestNumber;

      if (array.length > 1) {
          smallestNumber = Math.min(...array);
          finalArray.push(biggestNumber, smallestNumber);
      } else {
          finalArray.push(biggestNumber);
      }

      array = array.filter(a => a != biggestNumber);
      array = array.filter(a => a != smallestNumber);

  }

  console.log(finalArray.join(' '));
}

let input = [94, 1, 21, 3, 52, 69, 63, 31, 2, 18, 94];

let result = filterArray(input);
console.log(result);

function sorting(arr) {
  let highLowArr = [];
  let descendingArr = arr.sort((a, b) => b - a);

  let smallest = descendingArr.pop();
  let biggest = descendingArr.shift();

  while (smallest !== undefined || biggest !== undefined) {
    //Add to sorted array
    if (biggest !== undefined) {
      highLowArr.push(biggest);
    }

    if (smallest !== undefined) {
      highLowArr.push(smallest);
    }

    //Get new values from old arr
    smallest = descendingArr.pop();
    biggest = descendingArr.shift();
  }
  //Output
  console.log(highLowArr.join(' '));
}

let input2 = [94, 1, 21, 3, 52, 69, 63, 31, 2, 18, 94];

let result2 = sorting(input2);
console.log(result2);