JavaScript two objects - overriding each other

Question

I am trying to learn Object Oriented Programming in JavaScript. Therefore, I may be wrong in what I am doing.

I have one JS function (class):

function User() {
    //initiating object code goes here
}

//Functions
User.prototype.getEmpId = function() {
    return this.empId;
}

var myUser = new User({'empid':'1'});

console.log(myUser.getEmpId()); //Returns 1

var mynewuser = new User({'empid':'2'});

console.log(myUser.getEmpId()); //Returns 2

console.log(mynewuser.getEmpId()); //Returns 2

I don't understand what is going wrong here. If these two are two different objects then why is it causing problem. I have added the complete code here .

Thanks in advance.

Answer 1

User.prototype.getEmpId() {
  return this.empId;
}

should be

User.prototype.getEmpId = function () {
  return this.empId;
}

Answer 2

User.prototype.getEmpId gets overridden each time you instantiate the User object. The prototype property is shared between all instances.

Then what to do:

User.prototype.getEmpId = function() {
  return this.empId;
}

Answer 3

Check this fiddle :

http://jsfiddle.net/c5yhpav9/2/

function User(obj) {
//initiating object code goes here
this.empId=obj.empid;
}

//getEmpId now shared for all the instances of User
User.prototype.getEmpId=function() {
   return this.empId;
}

var myUser = new User({'empid':'1'});

alert(myUser.getEmpId()); //Returns 1

var mynewuser = new User({'empid':'2'});

alert(myUser.getEmpId()); //Returns 1

alert(mynewuser.getEmpId()); //Returns 2

Now gettting back to the problem you are facing in your sample shared. I found that you are setting properties/values on the User.prototype object itself each time a User object is instantiated. Rather, you should set on each instances of User . Following is the updated jsfiddle which works:

http://jsfiddle.net/L3qs4eg7/

Major Changes done:

first,

formUserObjectFromObject.call(this);//calling with reference of this

and,

function formUserObjectFromObject() {
    //Will only be called for one object.
    for (var userKey in arg[0]) {
        switch(userKey) {
            case "appId": 
                //Calling setAppId on this to set value of property
                this.setAppId(arg[0][userKey]);
                break;
            case "empId":
                this.setEmpId(arg[0][userKey]);
                break;
            case "firstName":
                this.setFirstName(arg[0][userKey]);
                break;
            case "lastName":
                this.setLastName(arg[0][userKey]);
                break;
            case "roleId":
                this.setRoleId(arg[0][userKey]);
                break;
            case "emailId":
                this.setEmailId(arg[0][userKey]);
                break;
            case "supervisorId":
                this.setSupervisorId(arg[0][userKey]);
                break;
            default:
                this.setCustom(userKey, arg[0][userKey]);
                break;
        }
    }
}

Hope that helps to understand!