trialDivision.js

/**
 * @param {number} number
 * @return {boolean}
 */
export default function trialDivision(number) {
  // Check if number is integer.
  if (number % 1 !== 0) {
    return false;
  }

  if (number <= 1) {
    // If number is less than one then it isn't prime by definition.
    return false;
  } else if (number <= 3) {
    // All numbers from 2 to 3 are prime.
    return true;
  }

  // If the number is not divided by 2 then we may eliminate all further even dividers.
  if (number % 2 === 0) {
    return false;
  }

  // If there is no dividers up to square root of n then there is no higher dividers as well.
  const dividerLimit = Math.sqrt(number);
  for (let divider = 3; divider <= dividerLimit; divider += 2) {
    if (number % divider === 0) {
      return false;
    }
  }

  return true;
}