continuation_fizzbuzz.js

// The goal here is to write fizzbuzz in such a
// way that adding new rules is as easy as defining
// a new predicate containing a number to check and
// return result.
//
// I want the changes to be easily made, in a single
// place, outside of the hard logic of the code
//
// I also want it so that there is no need for a special
// case for multiple predicates matching, e.g. `fizzbuzz`

// helper range function
function range(x) {
  return Array.from(Array(x+1).keys()).slice(1, this.length);
}

// define a function that allows us to define predicates
function predicate (y, str) {
  return function (x) {
    if (x % y === 0) {
      return str;
    }
  }
}

// list of predicates
var predicates = [
  function fizz (x) {
    return predicate(3, 'fizz');
  },
  function buzz (x) {
    return predicate(5, 'buzz');
  }
  // adding new predicates is pretty simple, and doesn't affect the rest of the code
];

// check each predicate against a given number
// building up a string of output
function check_predicates (x) {
  return predicates.map(function (fn) {
    return fn()(x);
  }).filter(function (vals) {
    return vals;
  }).join("");
}

function fizzbuzz(x) {
  // if there was output from the predicate functions
  // return that from the map, else return the number
  return range(x).map(function (n) {
    return (check_predicates(n) || n);
  })
}

// show what we've got
var output = fizzbuzz(35);

for(line of output) {
  console.log(line);
}