Calculating prime factors of a given number recursively @ Software Craftsmanship Berlin Meetup (2019-03-25)

recursively-calculate-prime-factor.js

/**
 * Calculates the prime factors for a given number.
 * - Note: Currently the function will chrash with numbers greater than ~2000 because of the recursive nature.
 * - This could potentially be optimized with e.g. proper tail calls
 *
 * @param {number} number - number used to calculate the prime factors
 * @returns {array} primeFactors
 */
function calculatePrimeFactor (number, prime = 2, results = []) {
  if (number >= prime && number % prime === 0) {
    results.push(prime)
    if (prime !== number) {
      return calculatePrimeFactor(number/prime, prime, results)
    } else return results
  } else if (number > prime) {
    return calculatePrimeFactor(number, prime+1, results)
  } else return results
}

/**
 * Test the primeFactor function
 *
 * @param {object} tests - the property is the number to test and the value is the expected result
 */
function runTests (tests) {
  let errors = 0
  Object.keys(tests).forEach(test => {
    const aim = tests[test].toString()
    const testResult = calculatePrimeFactor(Number(test)).toString()
    if (testResult !== aim) {
      errors++
      console.log(`FAIL: Expected ${aim} - got ${testResult}`)
    }
    else console.log(`OK: Expected ${aim} - got ${testResult}`)
  })
  
  if(errors > 0) throw 'test failed'
  console.log('test succeed')
}

runTests({
  0: [],
  1: [],
  2: [2],
  4: [2,2],
  6: [2,3],
  8: [2,2,2],
  11: [11],
  12: [2,2,3],
  16: [2,2,2,2],
  250: [2,5,5,5],
  275: [5,5,11],
  1111: [11,101],
  1122: [2,3,11,17],
  1987: [1987],
  // 105733: [105733] // this will chrash with RangeError: Maximum call stack size exceeded
})