Standard deviation func

stdev.js

/**
 * Calculates standrad deviation
 *
 * @param {Array} arr
 * @returns {number}
 */
function standradDeviation (arr) {
  const n = arr.length;
  const bias = Math.pow(arr.reduce((acc, v) => acc+v, 0)/n , 2);
  const s2 = arr.reduce((acc,v) => acc+(v*v-bias), 0)/(n-1);

  return Math.sqrt(s2);
}