quick and dirty javascript "lib" to prepare for a statistics exam

m.js

'use strict';

var _fstore = [];
function factorial (n) {
  if (n == 0 || n == 1) {
    return 1;
  }
  if (_fstore[n] > 0) {
    return _fstore[n];
  }
  return _fstore[n] = factorial(n - 1) * n;
}

module.exports = {
  binomial: (n, x, prob) => {
    if ((n >= x) && (prob <= 1) && (prob >= 0) && Number.isInteger(n) && Number.isInteger(x) && ( x >= 0)) {
      return (factorial(n) / (factorial(n - x) * factorial(x))) * Math.pow(prob, x) * Math.pow(1 - prob, n - x);
    } else {
      console.log("expected: n, x, p");
    }
  },
  factorial: factorial,
  distinguishable_sequence: obj => {
    if (obj !== null && typeof obj === 'object') {
      let values = Object.values(obj);
      if (values.every(Number.isInteger)) {
        let n = values.reduce((a, b) => a + b);
        let denum = values.reduce((a, b) => "" + a + "! " + b) + "!";
        console.log(n + "!");
        console.log("-".repeat(denum.length));
        console.log(denum);
        return factorial(n) / (values.reduce((a, b) => a * factorial(b)));
      }
    } else {
      console.log("expected object with string/integer pairs");
    }
  }
};