shabashj
4/19/2016 - 7:48 PM

Factory Method design pattern. Definition - Define an interface for creating an object, but let subclasses decide which class to instantiate

Factory Method design pattern. Definition - Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses. A Factory Method creates new objects as instructed by the client. One way to create objects in JavaScript is by invoking a constructor function with the new operator. There are situations however, where the client does not, or should not, know which one of several candidate objects to instantiate. The Factory Method allows the client to delegate object creation while still retaining control over which type to instantiate.

factory.js
content_copyfile_download
    function Factory() {
        this.createEmployee = function (type) {
            var employee;
     
            if (type === "fulltime") {
                employee = new FullTime();
            } else if (type === "parttime") {
                employee = new PartTime();
            } else if (type === "temporary") {
                employee = new Temporary();
            } else if (type === "contractor") {
                employee = new Contractor();
            }
     
            employee.type = type;
     
            employee.say = function () {
                log.add(this.type + ": rate " + this.hourly + "/hour");
            }
     
            return employee;
        }
    }
     
    var FullTime = function () {
        this.hourly = "$12";
    };
     
    var PartTime = function () {
        this.hourly = "$11";
    };
     
    var Temporary = function () {
        this.hourly = "$10";
    };
     
    var Contractor = function () {
        this.hourly = "$15";
    };
     
    // log helper
    var log = (function () {
        var log = "";
     
        return {
            add: function (msg) { log += msg + "\n"; },
            show: function () { alert(log); log = ""; }
        }
    })();
     
    function run() {
        var employees = [];
        var factory = new Factory();
     
        employees.push(factory.createEmployee("fulltime"));
        employees.push(factory.createEmployee("parttime"));
        employees.push(factory.createEmployee("temporary"));
        employees.push(factory.createEmployee("contractor"));
        
        for (var i = 0, len = employees.length; i < len; i++) {
            employees[i].say();
        }
     
        log.show();
    }