Strongly Typed Language to JavaScript

**Robert** · Jul 23 '05, 02:55 PM

Re: Strongly Typed Language to JavaScript

rpraveen@yahoo. com (Praveen Ramesh) wrote in message news:<4fd2ca58. 0410200812.7c72 2dde@posting.go ogle.com>...[color=blue]
> Hi,
>
> I just started writing a lot of script code in JavaScript (accessing
> browser DOM basically) and coming from the C#-VS.Net background, I
> just hate it. There is no true class definition support[/color]

Perhaps data encapsolation via closures would be helpful. Notice how
the variable accumulate is used.

Robert

<html>
<head>
<title>encapsol ated data</title>
<script type="text/javascript" >
function util()
{
// This is the encapsolated variable.

var accumulate = 0;

function add()
{
accumulate += 5;
show();
}

function show()
{
alert("accumula te = " + accumulate);
}

// Make know the inner functions.

util.add = add;
util.display = show;
}
</script>
</head>
<body>
<script type="text/javascript" >
// Initial
util();

util.add();
util.add();

util.display();
</script>
<p>We have Demonstrated encapsolated data through the use
of a closure.</p>
</body>
</html>

**lawrence** · Jul 23 '05, 03:11 PM

Re: Strongly Typed Language to JavaScript

rccharles@my-deja.com (Robert) wrote in message news:<c6bb75ff. 0410221154.6afb 1309@posting.go ogle.com>...[color=blue]
> rpraveen@yahoo. com (Praveen Ramesh) wrote in message
> <script type="text/javascript" >
> function util()
> {
> // This is the encapsolated variable.
>
> var accumulate = 0;
>
> function add()
> {
> accumulate += 5;
> show();
> }
>
> function show()
> {
> alert("accumula te = " + accumulate);
> }
>
> // Make know the inner functions.
>
> util.add = add;
> util.display = show;
> }
> </script>
> </head>
> <body>
> <script type="text/javascript" >
> // Initial
> util();
>
>
> util.add();
> util.add();
>
> util.display();
> </script>[/color]

I'm a newbie and still trying to get the syntax. What does this mean?
[color=blue]
> util.add = add;
> util.display = show;[/color]

If add() is a method then shouldn't it be followed by parenthesises?

**Michael Winter** · Jul 23 '05, 03:11 PM

Re: Strongly Typed Language to JavaScript

On 6 Nov 2004 09:24:36 -0800, lawrence <lkrubner@geoci ties.com> wrote:
[color=blue]
> rccharles@my-deja.com (Robert) wrote in message
> news:<c6bb75ff. 0410221154.6afb 1309@posting.go ogle.com>...
>[color=green]
>> <script type="text/javascript" >
>>
>> function util()
>> {
>> // This is the encapsolated variable.
>>
>> var accumulate = 0;
>>
>> function add()
>> {
>> accumulate += 5;
>> show();
>> }
>>
>> function show()
>> {
>> alert("accumula te = " + accumulate);
>> }
>>
>> // Make know the inner functions.
>>
>> util.add = add;
>> util.display = show;
>> }
>> </script>
>> </head>
>> <body>
>> <script type="text/javascript" >
>> // Initial
>> util();
>>
>>
>> util.add();
>> util.add();
>>
>> util.display();
>> </script>[/color]
>
> I'm a newbie and still trying to get the syntax. What does this mean?[/color]

The first thing to understand is that a function is an object, just a
special type that can be "called". Like other objects, it can have
properties and in the code above, properties are added to this object.

The second is related to the first. As you may, or may not, be aware,
objects are accessed via references. This means that two or more
identifiers can refer to the same object, and any change made through one
reference is reflected through all other identifiers that refer to the
same object. Perhaps some code in order here:

// Both myObj and myRef will refer to the same object
var myObj = new Object(),
myRef = myObj;

myObj.member = 'a string'; // assign through first reference

alert(myObj.mem ber); // 'a string';
alert(myRef.mem ber); // also 'a string';

myRef.member = 15; // assign through the second reference

alert(myObj.mem ber); // 15;
alert(myRef.mem ber); // also 15;

So, extending this to functions:

function myFunction() {
alert('called myFunction');
}

var myRef = myFunction;

myRef(); // alerts 'called myFunction'

Hopefully that's laid some groundwork.

In the function, util, two inner functions, add and display, are defined.
Inner functions act just like local variables: they are not visible
outside the scope of the outer function that declares them.
[color=blue][color=green]
>> util.add = add;
>> util.display = show;[/color]
>
> If add() is a method then shouldn't it be followed by parenthesises?[/color]

What the code does in this instance is make the inner functions properties
of the outer function. Like I've shown previously, those two lines create
two references to the inner functions. Because you aren't actually calling
the functions - there are no parentheses - you are assigning the
*function* to the property, not the result of the function.

However, I don't think I like that particular production much as calling
util again will reset the data. If that's intended, then fine. If not,

var util = (function() {
var accumulate = 0;

return {
add : function(n) {accumulate += n;},
show : function() {alert(accumula te);}
};
})();

would be better as the setup is a one-time-only process.

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.

**lawrence** · Jul 23 '05, 03:20 PM

Re: Strongly Typed Language to JavaScript

"Michael Winter" <M.Winter@bluey onder.co.invali d> wrote in message news:<opsg2di2t dx13kvk@atlanti s>...[color=blue]
>The first thing to understand is that a function is an object, just a
>special type that can be "called". Like other objects, it can have
>properties and in the code above, properties are added to this[/color]
object.

Are there any other computer languages where you can add a property to
a class after the class has been defined? I know in Ruby you can add
even methods to a class at run-time, so I suppose Ruby allows you to
add class properties as well. But are there any others? I'm used to
the idea of a class being defined, and then remaining fixed for the
rest of its life.

**lawrence** · Jul 23 '05, 03:20 PM

Re: Strongly Typed Language to JavaScript

"Michael Winter" <M.Winter@bluey onder.co.invali d> wrote in message news:<opsg2di2t dx13kvk@atlanti s>...[color=blue]
> function myFunction() {
> alert('called myFunction');
> }
>
> var myRef = myFunction;
>
> myRef(); // alerts 'called myFunction'[/color]

I see. So myFunction(), with parenthesises causes the function to
fire, but myFunction, without parenthesises, passes a reference to
that function and allows one, thereafter, to treat it as an object?

**Grant Wagner** · Jul 23 '05, 03:20 PM

Re: Strongly Typed Language to JavaScript

lawrence wrote:
[color=blue]
> "Michael Winter" <M.Winter@bluey onder.co.invali d> wrote in message news:<opsg2di2t dx13kvk@atlanti s>...[color=green]
> > function myFunction() {
> > alert('called myFunction');
> > }
> >
> > var myRef = myFunction;
> >
> > myRef(); // alerts 'called myFunction'[/color]
>
> I see. So myFunction(), with parenthesises causes the function to
> fire, but myFunction, without parenthesises, passes a reference to
> that function and allows one, thereafter, to treat it as an object?[/color]

myFunction not "treated as an object", it is a reference to a Function object. The same as any other
reference to any other object.

var a = new Object();
var b = a; // both -b- and -a- point to the same object
b.one = 1;
alert(a.one); // 1

var a = function() {
alert('function -a-');
}
// same as:
// function a() {
// alert('function -a-');
// }
b = a; // both -b- and -a- point to the same object (function)
b();

So:
window.onload = function() { alert('loaded') ; }
or:
function a() { alert('loaded') ; }
window.onload = a;

constructs a new (anonymous in the first case) Function object and assigns the reference to that Function
object to the -onload- property of the -window-. When the document finishes loading, the host environment
invokes the Function object referenced by the -onload- property of the -window- object.

--
Grant Wagner <gwagner@agrico reunited.com>
comp.lang.javas cript FAQ - http://jibbering.com/faq

**Michael Winter** · Jul 23 '05, 03:20 PM

Re: Strongly Typed Language to JavaScript

On 16 Nov 2004 09:17:56 -0800, lawrence <lkrubner@geoci ties.com> wrote:

[snip]
[color=blue]
> Are there any other computer languages where you can add a property to a
> class after the class has been defined?[/color]

Javascript isn't class-based. I could give a comparison, but that would
take a long time, particularly if I went into inheritance techniques.
Instead, take a look at Douglas Crockford's web site
(<URL:http://www.crockford.c om/>). The "survey" covers the main elements
of the language, and other articles examine more advanced areas in detail.
[color=blue]
> I know in Ruby you can add even methods to a class at run-time, so I
> suppose Ruby allows you to add class properties as well. But are there
> any others?[/color]

I couldn't comment on Ruby as I haven't used it. However, I am familiar
with several programming languages, and ECMAScript is the only truly
dynamic one among them.

[snip]

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.

**Michael Winter** · Jul 23 '05, 03:20 PM

Re: Strongly Typed Language to JavaScript

On 16 Nov 2004 09:30:41 -0800, lawrence <lkrubner@geoci ties.com> wrote:
[color=blue]
> "Michael Winter" <M.Winter@bluey onder.co.invali d> wrote in message
> news:<opsg2di2t dx13kvk@atlanti s>...
>[color=green]
>> function myFunction() {
>> alert('called myFunction');
>> }
>>
>> var myRef = myFunction;
>>
>> myRef(); // alerts 'called myFunction'[/color]
>
> I see. So myFunction(), with parenthesises causes the function to fire,[/color]

Correct.
[color=blue]
> but myFunction, without parenthesises, passes a reference to that
> function and allows one, thereafter, to treat it as an object?[/color]

I'm not sure that you've understood. There is no "passing of a reference",
and a function *is* an object, just a special kind that can be "called".
Perhaps I'm just attaching meaning to the words that you didn't intend
(that's why using the right vocabulary is important).

Functions can have properties just like any other object. Functions can
even have methods. The only thing that makes them different to "regular"
objects is that when you put () after the reference, you can have it
execute code.

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.

**Richard Cornford** · Jul 23 '05, 03:20 PM

Re: Strongly Typed Language to JavaScript

lawrence wrote:[color=blue]
> Michael Winter wrote:[color=green]
>> The first thing to understand is that a function is an object,
>> just a special type that can be "called". Like other objects,
>> it can have properties and in the code above, properties are
>> added to this object.[/color]
>
> Are there any other computer languages where you can add a
> property to a class after the class has been defined?[/color]

Javascript doesn't have classes. By ECMA specification all objects
(except host objects) are of the same; The ECMAScript native object.
That object allows the dynamic creation of new properties at run time.
Objects that have been modified in the same way (either internally by
the interpreter or by script code) can be conceived as belonging to a
distinct 'class' , but that would be done for the convenience of the
author and would not represent a real imposition on the objects.

<snip>[color=blue]
> I'm used to the idea of a class being defined, and
> then remaining fixed for the rest of its life.[/color]

When you have more experience of cross-browser scripting you will
appreciate the advantages of having a truly dynamic language in which to
write them.

Richard.

Strongly Typed Language to JavaScript

Strongly Typed Language to JavaScript

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment