JavaScript - Passing Object By Reference Question

Hi,

I've had problems in the past understanding this, however, after reading this tutorial, I understand. In some languages, like VB6, I notice the "byVal" and the "byRef" is specifically used. In javascript, I don't notice those specifics typed in functions. Is the "default" by value when using in a function to change a parameter? If it is, what is the syntax for using by reference, or is that ever used?

My question arises from this notation taken from here:

Quote:
Note that it is the value that a has at the time that it is passed into the function that gets substituted into the argument and not the value that the original variable has at that point in the processing. It is the values in the parameters that the function uses and not the variables. This is called pass by value . In those languages where you can pass the actual variable into the function instead of just passing its value the method used to do so is called pass by reference . Had we been able to pass the variables into the function by reference rather than by value then the final value in b would have been -16 instead of -14.
Here is the example (passing by value):

Code:

function myfunction(y, z) {
  a += y;
  b -= z;
}


var a = 0;
var b = 10;
var c = 3;
var d = 4;
var e = 2;
myfunction(c, d);
myfunction(d, e);
myfunction(9, 2);
myfunction(b, a);

Results:
myFunction(c, d);	output:  0 +  3 = 3(y), 10 - 4 = 6(z)
myFunction(d, e);	output:  3 +  4 = 7(y),  6 - 2 = 4(z) 
myFunction(9, 2);	output:  7 +  9 = 16(y), 4 - 2 = 2(z)
myFunction(b, a);	output:  2 + 16 = 18(y), 2 -16 = -14(z)

Thanks!

The goal is for selectedDay to be assigned the value of the system variable Mainpackage.subclass0.subclass1.firstDay and then incremented by two days. Mainpackage.subclass0.subclass1.firstDay needs to be unchanged.

Important system variable in red.
To be 'manipulated and used' variable in green.
Even with an intermediary, third, dummy variable it doesn't work:

Code:

    
//Declarations and instantiations
    var  systemDate  = new Date();
    var  selectedDay  = new Date();
     Mainpackage.subclass0.subclass1.firstDay ;
//Assignments and manipulations
     systemDate  =  Mainpackage.subclass0.subclass1.firstDay ;
     selectedDay  =  systemDate ;
     selectedDay .setDate( selectedDay .getDate()+2);
//Logging
    console.log('Mainpackage.subclass0.subclass1.firstDay: ' +Mainpackage.subclass0.subclass1.firstDay +'\n' +'systemDate: ' +systemDate +'\n' +'selectedDay :' +selectedDay +'\n');

Console log is:
Code:

Mainpackage.subclass0.subclass1.firstDay: Tue Aug 24 2010 00:00:00 GMT-0400 (Eastern Daylight Time) 
systemDate: Tue Aug 24 2010 00:00:00 GMT-0400 (Eastern Daylight Time) 
selectedDay: Tue Aug 24 2010 00:00:00 GMT-0400 (Eastern Daylight Time)

It doesn't work in my webapp : All variables change at the same time.

Hi, I have this ajax routine...

Code:

function xhr_get(target_str,async){
	var sync=true;
	if(async){sync=false;}
	var xhr = new XMLHttpRequest();
	xhr.open('GET', target_str, sync);	
	if(sync==false){
		xhr.onreadystatechange = function () {
			if (xhr.status === 200) {
				try{ var ii =JSON.parse(xhr.responseText);} catch (exception) { }
				if(ii){	return ii; }else{ alert(xhr.responseText); return false; }
			} else {
					alert(xhr.status+'  '+target_str);return false;
			}
		};
		xhr.send(null);
	}else{
		xhr.send(null);
		try{ var ii =JSON.parse(xhr.responseText);} catch (exception) { }
		if(ii){ return ii; }else{ alert(xhr.responseText); return false; }
	}
}

now if I alert(ii) on success the data I am looking for (specifically ii.content) shows up in the alert as expected
however when calling from another javascript function, ii is false ???? please explain,

Code:

function call_change_val(fld,vm_id){
	var str='?_f=load_edit_fld&_ctl_fld='+fld+'&vm_id='+vm_id+'&fld='+fld+'&width=80';
	i = xhr_get('ajax/val_main_loader.php'+str,true);

    //////////////////////    alert(i); or alert(i.content) here both give be a blank popup/////////////////

	showdiv('c_change_'+fld);
	setih('c_change_'+fld,i.content);
}

I expected alert(i) to say Object or similar, getting nothing

I am confused about what the return keyword is actually returning when returning an object, a primitive, or a function.

My confusion is compounded by the fact that I'm not sure if a function is an object or not.
According to the book JavaScript Programmer Reference it is:
"All functions in JavaScript are first class objects , meaning they can be passed around like any other object reference. In fact, regardless of how they are created, functions are instances of a global object named (aptly) Function."

However, someone else states that a function is not an object. An object is a set of primitives and references. A function is executable code. Functions become objects through the use of the new operator. Yet, in the book I mentioned, it says you don't need the new keyword to execute the function as an object, as it already inherits from the object Function when the function keyword is used:
Code:

function functionName([argname1 [, ...[, argnameN]]])
{
statements;
}

So there's one source of contradiction.

Now the bigger issue is what is going on when the return keyword is used. Notice the Validation() function returns an object as its last expression. This technique is common, where you return an object which contains functions in form of object notation. I believe this is done so that we create a closure so that when the intepreter exits the Validation() method, since we created a closure by returning an object, which contains the inner functions addRule and getRule, the local variables of Validation() are not destroyed, given that we can reference them through the two inner functions that make use of the local variables of the outer function. So when we use the return keyword on an object literal, and then exit the function, when we call one of the inner functions as we do later:
Code:

var rule = $.Validation.getRule(types[type]);

essentially getRule() is called, passes an argument, which is received by the inner function as parameter we call name:
Code:

getRule : 
function(name) {  

                return rules[name];
            }

First, note that the return {} is written in object notation, therefore making getRule a local variable and, thus, private function only accessible through the namespace of Validation().

Validation() declares the rules local variable and because of the closure, we can access the rules local variable through the getRule() inner function.

*****Here's the part that really thows me off. We return rules[name]. So let's say name is equal to email. This is an associative array so email (held in name) is a property of rules. So here we return the object's property:
Code:

return rules[name];

And then assign it to a local variable called rule:
Code:

var rule = $.Validation.getRule(types[type]);

So when we return an object rules[name], do we return a reference to an object or a value? In other words, by returning rules[name], where name is equal to email, are we then returning a reference to the following object literal:
Code:

email : {
               check: function(value) {
                   
                   if(value)
                       return testPattern(value,".+@.+\..+");
                   return true;
               },
               msg : "Enter a valid e-mail address."
            }

And if we are returning a reference, by returning a reference, are we essentially pointing to this object when we assign it to rule? In other words, the variable rule is just pointing to the object literal?

And is that the reason we can then access the check function or msg local variable through rule using dot notation, because rule points to the email object literal?

Now the ultimate brain twist for me is that if a function is an object, then why when return a function, it returns a value, such as a boolean, if an object only returns a reference and not the value?

Code:

//Validation is a local variable as it is in a self-executing anonymous function. The purpose of the said anonymous function is to pass the jQuery object as a parameter $ so the $() function will be in scope of the anonymous function and not interfere with other libraries that make use of the same function technique - in the global scope. 
(function($) {
        var rules = {
            
            email : {
               check: function(value) {
                   
                   if(value)
                       return testPattern(value,".+@.+\..+");
                   return true;
               },
               msg : "Enter a valid e-mail address."
            },
            url : {

               check : function(value) {

                   if(value)
                       return testPattern(value,"https?://(.+\.)+.{2,4}(/.*)?");
                   return true;
               },
               msg : "Enter a valid URL."
            },
            required : {
                
               check: function(value) {

                   if(value)
                       return true;
                   else
                       return false;
               },
               msg : "This field is required."
            }
        }
        var testPattern = function(value, pattern) {

            var regExp = new RegExp("^"+pattern+"$","");
            return regExp.test(value); //The test() method is built into javascript
        }
        return {
            
            addRule : function(name, rule) {  

                rules[name] = rule;
            },
            getRule : function(name) { 

                return rules[name];
            }
        }
    }
    
    /* 
    Form factory 
    */
    var Form = function(form) {
        
        var fields = [];
    
        $(form[0].elements).each(function() {
            var field = $(this);
            if(field.attr('validation') !== undefined) {
                fields.push(new Field(field));
            }
        });
        this.fields = fields;
    }
    Form.prototype = {
        validate : function() {

            for(field in this.fields) {
                
                this.fields[field].validate();
            }
        },
        isValid : function() {
            
            for(field in this.fields) {
                
                if(!this.fields[field].valid) {
            
                    this.fields[field].field.focus();
                    return false;
                }
            }
            return true;
        }
    }
    
    /* 
    Field factory 
    */
    var Field = function(field) {

        this.field = field;
        this.valid = false;
        this.attach("change");
    }
    Field.prototype = {
        
        attach : function(event) {
        
            var obj = this;
            if(event == "change") {
                obj.field.bind("change",function() {
                    return obj.validate();
                });
            }
            if(event == "keyup") {
                obj.field.bind("keyup",function(e) {
                    return obj.validate();
                });
            }
        },
        validate : function() {
            
            var obj = this,
                field = obj.field,
                errorClass = "errorlist",
                errorlist = $(document.createElement("ul")).addClass(errorClass),
                types = field.attr("validation").split(" "),
                container = field.parent(),
                errors = []; 
            
            field.next(".errorlist").remove();
            for (var type in types) {

                var rule = $.Validation.getRule(types[type]);
                if(!rule.check(field.val())) {

                    container.addClass("error");
                    errors.push(rule.msg);
                }
            }
            if(errors.length) {

                obj.field.unbind("keyup")
                obj.attach("keyup");
                field.after(errorlist.empty());
                for(error in errors) {
                
                    errorlist.append("<li>"+ errors[error] +"</li>");        
                }
                obj.valid = false;
            } 
            else {
                errorlist.remove();
                container.removeClass("error");
                obj.valid = true;
            }
        }
    }
    
    /*
    Validation extends jQuery prototype
    */
    $.extend($.fn, {
        
        validation : function() {
            
            var validator = new Form($(this));
            $.data($(this)[0], 'validator', validator);
            
            $(this).bind("submit", function(e) {
                validator.validate();
                if(!validator.isValid()) {
                    e.preventDefault();
                }
            });
        },
        validate : function() {
            
            var validator = $.data($(this)[0], 'validator');
            validator.validate();
            return validator.isValid();
            
        }
    });
    $.Validation = new Validation();
})(jQuery);

Thanks for any response.

I have the following code:
[CODE]
rtn += "<div class='crowelem' style='width:100px;'>"+panel.genSendButton(current.readNode())+"</div>";
[CODE]
This is in a loop that generates rows in a DIV. current.readNode() is returning an object from a linked list, the method genSendButton looks like this:

[CODE]
MatchRequest.prototype.genSendButton = function (obj) {
var rtnstr = null;
if(obj.msNotified == 0) {
rtnstr = "<input type='button' value = 'Notify' onClick=\"javascriptanel.sendNotification("+obj+")\"/>";
} else {
rtnstr = "<input type='button' value='Already Notified' disabled='true' onClick=\"javascriptanel.sendNotification('"+obj.msID+"')\"/>";
}
return(rtnstr) ;
}
[CODE]
If you step into this code in a debugger, obj is correctly passed into genSendButton as an object of the appropriate class. The code in the if(obj.msNotified == 0) clause generates an error. The var obj resolves to NPanlel: (this happens to be the class of the object). Regardless of how I try to pass obj into the method sendNotification it doesn't resolve to an object. Can anyone shed any light on where my omission of intelligence is occurring?

Any help would be greatly appreciated.

Mrbub