js demo

plan.js

var Plan = (function() {

  // protected
  var records = [];

  // the Plan constructor
  function Plan(id, price) {
    this.id = id;
    this.price = price;
    records.push(this);
  }

  // Plan instance methods go here
  Plan.prototype = {
    formattedPrice: function() {
      if (isNaN(this.price)) {
        return this.price;
      } else {
        return "$" + this.price + ".00";
      }
    }
  };

  // "Class" methods
  Plan.find = function(id) {
    var result = records.filter(function(record) {
      return record.id === id;
    });
    return result.length ? result[0] : null;
  };

  Plan.all = function() {
    return records;
  };

  return Plan;

}());

new Plan(1,"FREE");
new Plan(2,5);
new Plan(3,10);
new Plan(4,100);
new Plan(5,1000);

console.log("All Plans: ", Plan.all());
console.log("Plan with id 4:", Plan.find(4));
console.log("Formatted price of plan with id 4:", Plan.find(4).formattedPrice());