A Javascript function to filter an array of values for outliers by using an interquartile filter

outliersFilter.js

function filterOutliers(someArray) {

  if(someArray.length < 4)
    return someArray;

  let values, q1, q3, iqr, maxValue, minValue;

  values = someArray.slice().sort( (a, b) => a - b);//copy array fast and sort

  if((values.length / 4) % 1 === 0){//find quartiles
    q1 = 1/2 * (values[(values.length / 4)] + values[(values.length / 4) + 1]);
    q3 = 1/2 * (values[(values.length * (3 / 4))] + values[(values.length * (3 / 4)) + 1]);
  } else {
    q1 = values[Math.floor(values.length / 4 + 1)];
    q3 = values[Math.ceil(values.length * (3 / 4) + 1)];
  }

  iqr = q3 - q1;
  maxValue = q3 + iqr * 1.5;
  minValue = q1 - iqr * 1.5;

  return values.filter((x) => (x >= minValue) && (x <= maxValue));
}