Factorials, Permutations & Combinations

A simple node.js library that computes basic

• Factorials
• Permutations
• Combinations

Prerequisites

• Node.js is required to run the library
• Mocha is used for testing

Using the Modules

• factorials.js - modules check input is positive integers and 0.

  • getFactorial (n)
    • returns n! for valid n
  • getPartialPerm (n, k)
    • returns partial permutation for valid n, k
  • combination (n, k)
    • returns n choose k for valid n,k

  // factorials.js exports
  
  module.exports = {
    getFactorial: getFactorial,
    getPartialPerm: getPartialPerm,
    combination: combination
  }
  

  • import into your file

  // import modules and use
  
  const facts = require('./factorials');
  
  let x = facts.getFactorial(5);    // x = 120
  x = facts.getPartialPerm(5, 3);   // x = 60
  x = facts.combination(5, 3);      // x = 10
  

• useFactorials.js - example code to use the library

  • run from the command line with input

  $ node useFactorials.js 5 3
  

  • output

  factorial of 5 is: 120
  partial permutation of 5,3 is: 60
  combination of 5,3 is: 10
  

Testing

• test.js - contains the tests.

  // Multiple ways to run test.js
  $ mocha
  $ mocha test
  $ mocha --reporter=nyan   // for the rainbow space cat nyan
  $ npm test
  

Motivation

• learn unit testing
• learn Mocha
• learn Node.js

Acknowledgements

• Tania Rascia's Unit Testing in JavaScript with Mocha

Author

• Betsy Stevens