fluent arithmetic operators

operable.js

// 9 July 2015
// operable: add, subtract, multiply, divide, remainder
// 19 Dec 2017: added valueOf() vs. toString()

function operable(value) {
  var c = Object.create(operable.prototype);
  c.toString = function() {
    return '' + value;
  };
  c.valueOf = function() {
    return value;
  };
  return c;
};

operable.prototype = {
  'add'       : function add(n) {       return isNaN(this) ? NaN : +this + n; },
  'subtract'  : function subtract(n) {  return this - n; },
  'multiply'  : function multiply(n) {  return this * n; },
  'divide'    : function divide(n) {    return this / n; },
  'remainder' : function remainder(n) { return this % n; }
};

console.warn('*** operable ***');
console.log( operable(0).add(-0) );
console.log( operable(3).add(3) );
console.log( operable(-3).subtract(3) );
console.log( operable(-3).multiply(3) );
console.log( operable(-3).divide(3) );
console.log( operable(-9).remainder(4) );

console.log( operable(1).add(true) );
console.log( operable(false).add(false) ); // ?
console.log( operable(3).add('3') );
console.log( operable(3).subtract('3') );
console.log( operable(9.5).remainder('.75') );

console.warn('*** Infinity ***');
console.warn( operable(1).divide(0) );
console.warn( operable(1).divide('0') );
console.warn( operable('1').divide('0') );
console.warn( operable('1').divide(0) );

console.warn('*** NaN ***');
console.log( operable('false').add(false) );
console.log( operable('bogus').subtract(6) );
console.log( operable(6).subtract('f') );
console.log( operable(6).multiply('f') );
console.log( operable(9.5).remainder('christ') );

console.warn('*** toString vs. valueOf ***');
console.log( operable(7).toString() === '7' );
console.log( operable(7).valueOf() === 7);