Singleton Constructor Factory

singleton-factory-examples.js

function Box(x,y) {
  this.x = x;
  this.y = y;
}

var Box1 = Singleton(Box, { argumentCheck: 'equal'});
var Box2 = Singleton(Box, { argumentCheck: 'equal'});

var obj1 = new Box1(1,2);
var obj2 = new Box2(1,2);
var obj3 = new Box1(1,2);

console.log('obj1 === obj2', obj1 === obj2);
console.log('obj1 === obj3', obj1 === obj3);
console.log('obj2 === obj3', obj2 === obj3);

var SomeService = Singleton(function() {
  return {
    funcOne: function() {
      console.log('funcOne');
    },
    funcTwo: function(text) {
      console.log(text || 'No text provided.');
    }
  };
}, { argumentCheck: 'less' });

var service1 = new SomeService();
var service2 = new SomeService();
console.log('service1 === service2', service1 === service2);

var service3 = new SomeService({ someOption: true });

singleton-factory.js

function Singleton(obj, options) {
  
  var defaultOptions = {
    ignoreArgumentUniqueness: false,
    defaultHash: 'asdfii12300fkadfn213if0',
    argumentCheck: 'none' // 'none', 'less', 'equal',
  };
  
  function mergeObjects(obj1, obj2) {
    var obj3 = {};
    for (var attrname1 in obj1) { obj3[attrname1] = obj1[attrname1]; }
    for (var attrname2 in obj2) { obj3[attrname2] = obj2[attrname2]; }
    return obj3;
  }
  
  options = mergeObjects(defaultOptions, options);
  
  var __instances = {};
  return function() {
    var args = Array.prototype.slice.call(arguments);
    
    if (!options.ignoreArgumentUniqueness && options.argumentCheck === 'less') {
      if (args.length > obj.length) {
        throw new Error('Too many arguments provided. Expected: ' + obj.length + '. Actual: ' + args.length + '.');
      }
    }
    
    if (!options.ignoreArgumentUniqueness && options.argumentCheck === 'equal') {
      if (args.length !== obj.length) {
        var manyOrFew = args.length > obj.length ? 'many' : 'few';
        throw new Error('Too ' + manyOrFew + ' arguments provided. Expected: ' + obj.length + '. Actual: ' + args.length + '.');
      }
    }
    
    var argHash = options.ignoreArgumentUniqueness ? options.defaultHash : JSON.stringify(args);

    if (!__instances.hasOwnProperty(argHash)) {
    
      var createObj = function() {
        return obj.apply(this, args);
      };
    
      createObj.prototype = obj.prototype;
      
      __instances[argHash] = new createObj();
    }
    return __instances[argHash]; 
  };
    
};