function sortEvenOdds(myArray){
  var arrEvens = [];
  var arrOdds = [];
  for (var i = 0; i < myArray.length ; i++) {
    if (myArray[i] % 2 === 0 ) {
      arrEvens.push(myArray[i]);
    }
    else arrOdds.push(myArray[i]);
    }
  return [arrOdds, arrEvens];
}

var myArray = [1,2,3,4,5,6,7,8];
sortEvenOdds(myArray);

// [ [ 2 ,4, 6 ], [ 1, 3, 5 ] ]