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Why wont this script work?

 
 
Ali
Guest
Posts: n/a
 
      09-30-2004
I have the following web page with a script in it.

<html>

<head>

<title>Make Your Own Objects test</title>

<script>

function info(self,n,e) {

function showInfo(self,nam, ema) {

document.write("<hr>");

document.write("<b>Name: </b>"+nam);

document.write("<b>Email: </b>"+ema);

}

self.name = n;

self.email= e;
self.show() = showInfo(self.name,self.email);

}

</script>

</head>

<body>

<script>

ali = info("Ali","(E-Mail Removed)");

zainab = info("Zainab","(E-Mail Removed)");


ali.show();
zainab.show();

</script>

</body>

</html>

I want the script to make two objects: ali and zainab. These objects
are to have two properties (name and email) and a method (show). The
show method is supposed to display the other two properties of the
object.

Please Help. Thank You.
 
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Lee
Guest
Posts: n/a
 
      09-30-2004
Ali said:
>
>I have the following web page with a script in it.


>I want the script to make two objects: ali and zainab. These objects
>are to have two properties (name and email) and a method (show). The
>show method is supposed to display the other two properties of the
>object.


Is this for a class, or are you trying to learn Javascript on your own?
Are you working from some sort of textbook or online tutorial?

 
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Thomas 'PointedEars' Lahn
Guest
Posts: n/a
 
      10-17-2004
Ali wrote:

> <html>


The DOCTYPE declaration is missing prior to this start tag, e.g.

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>

> [...]
> <script>

^
The "type" attribute is missing:

<script type="text/javascript">

> function info(self,n,e) {
>
> function showInfo(self,nam, ema) {


Nested functions are not allowed in ECMAScript and implementations.
However, it is supported in JavaScript 1.5. The question probably
answered below is: Why do you consider it necessary here?

> document.write("<hr>");
>
> document.write("<b>Name: </b>"+nam);
>
> document.write("<b>Email: </b>"+ema);
>
> }
>
> self.name = n;


`self' refers to the current `window' object as this object is virtually
identical with the global object where the `self' property is available.
Assigning a value to its `name' property may not be possible. Most
certainly you are looking for `this.name'.

> self.email= e;
> self.show() = showInfo(self.name,self.email);

^^
The call operator may only be used right hand side in JavaScipt,
ECMAScript and its implementations.

> }
>
> [...}
> <script>


See above.

> ali = info("Ali","(E-Mail Removed)");
> zainab = info("Zainab","(E-Mail Removed)");


Variables should be declared, using the `var' keyword:

var ali = ...;
var zainab = ...;

Assuming that "info" is the constructor of an object, the proper syntax is

var ali = new info("Ali", "(E-Mail Removed)");
var ali = new info("Zainab","(E-Mail Removed)");

> ali.show();
> zainab.show();>


However, if show() ought to be a method of "info" objects, the proper syntax
is

function info(n, e)
{
this.show = function info_show()
{
// escape ETAGO if used in HTML context
document.write("<hr>"
+ "<b>Name: <\/b>" + this.name
+ "<b>Email: <\/b>" + this.email);
}

// consider ... = x || ""; for a default value
this.name = n;
this.email = e;
}

or better if info_show() does not contain a closure:

function info(n, e)
{
// see above
this.name = n;
this.email = e;
}

info.prototype.show = function info_show()
{
document.write("<hr>"
+ "<b>Name: <\/b>" + this.name
+ "<b>Email: <\/b>" + this.email);
}

However, document.write() is not a proper method to output information
after the document has been loaded. It may add information to the
document temporarily or it may overwrite the entire document, including
the functions defined therein. Ask Google Groups for proper solutions.

To avoid confusion and undesired side effects with built-in properties,
good code style recommends to let constructor identifiers begin with an
uppercase letter:

function Info(...)
{
...
}

> [...]
> I want the script to make two objects: ali and zainab. These objects
> are to have two properties (name and email) and a method (show). The
> show method is supposed to display the other two properties of the
> object.


And most certainly, you should have added that the properties
of the second object are not displayed (as expected).

"Does not work" is a useless error description. [psf 4.11]

Please read the FAQ before posting.


PointedEars
--
As the "BugFree(tm)" series didn't turn out so well, i'm starting a new
series called "ItWorksForMe(tm)" of which this new (browser) is yet another
shining example...
 
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John G Harris
Guest
Posts: n/a
 
      10-17-2004
In article <(E-Mail Removed)>, Thomas 'PointedEars'
Lahn <(E-Mail Removed)> writes

<snip>
>Nested functions are not allowed in ECMAScript and implementations.
>However, it is supported in JavaScript 1.5.

<snip>

It is allowed in ECMAScript v3, which has been around for over four
years.

John
--
John Harris
 
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Thomas 'PointedEars' Lahn
Guest
Posts: n/a
 
      10-17-2004
John G Harris wrote:

> In article <(E-Mail Removed)>, Thomas 'PointedEars'
> Lahn <(E-Mail Removed)> writes


Please stop posting attribution novels; the reasons have been explained
(to you) several times before.

>> Nested functions are not allowed in ECMAScript and implementations.
>> However, it is supported in JavaScript 1.5.

>
> It is allowed in ECMAScript v3, which has been around for over four
> years.


I'd be happy to be wrong here and read about the required productions
from the ECMAScript 3 grammar in a posting of you.


PointedEars
--
Dance, Mozilla, Dance!
 
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Randy Webb
Guest
Posts: n/a
 
      10-17-2004
Thomas 'PointedEars' Lahn wrote:

> John G Harris wrote:
>
>
>>In article <(E-Mail Removed)>, Thomas 'PointedEars'
>>Lahn <(E-Mail Removed)> writes

>
>
> Please stop posting attribution novels; the reasons have been explained
> (to you) several times before.


Considering that you are the only one that explains it, and you
generally and 100% explain it wrongly, thats just more of your unfounded
garbage spouting.

--
Randy
comp.lang.javascript FAQ - http://jibbering.com/faq
 
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Michael Winter
Guest
Posts: n/a
 
      10-17-2004
On Sun, 17 Oct 2004 23:26:27 +0200, Thomas 'PointedEars' Lahn
<(E-Mail Removed)> wrote:

> John G Harris wrote:
>
>> In article <(E-Mail Removed)>, Thomas 'PointedEars'
>> Lahn <(E-Mail Removed)> writes


[snip]

>>> Nested functions are not allowed in ECMAScript and implementations.
>>> However, it is supported in JavaScript 1.5.

>>
>> It is allowed in ECMAScript v3, which has been around for over four
>> years.

>
> I'd be happy to be wrong here and read about the required productions
> from the ECMAScript 3 grammar in a posting of you.


Will I do?

Unless I'm missing something major (quite possible as I don't have this
thread in full), you seem to be suggesting that

function a() {
function b() {
}
}

is illegal. Is that correct? Well, in a code example, section 13.2 -
Creating Function Objects, they have written almost precisely the above.

If you want the associated grammar:

FunctionDeclaration :
function Identifier ( FormalParameterListopt ) { FunctionBody }

FunctionBody :
SourceElements

SourceElements :
SourceElement
SourceElements SourceElement

SourceElement :
Statement
FunctionDeclaration

That suggests to me that it is perfectly legal to nest functions to any
degree. I haven't checked to any great extent to see if the text notes
limitations or exceptions, but I doubt there are any.

One thing I had noticed in the grammar is that you may not place function
declarations directly within a statement. As far as I can see, function
statements may only occur in:

- The program source at the "root" level.
- Other functions (expressions or statements).
- An eval() argument.

That would make something like:

if(...) {
function myFunction() {
}
}

illegal. However, a quick test shows that (at least some) browsers support
it. Why you'd do something like this, though, is another question.

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.
 
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Richard Cornford
Guest
Posts: n/a
 
      10-18-2004
Michael Winter wrote:
> On Sun, 17 Oct 2004 23:26:27 +0200, Thomas 'PointedEars' Lahn
> <(E-Mail Removed)> wrote:
>> John G Harris wrote:
>>> In article <(E-Mail Removed)>, Thomas
>>> 'PointedEars' Lahn <(E-Mail Removed)> writes

<snip>
>>>> Nested functions are not allowed in ECMAScript and
>>>> implementations. However, it is supported in JavaScript 1.5.


Nested function declarations and function expressions are supported by
Netscape 4 with JavaScript 1.3 and IE 4 (approx: JScript 2), about the
oldest browsers that remain viable as scriptable Internet user agents
(certainly the oldest considered for active support in a commercial
context, and often not then).

As is not unusual for such documents, the 3rd edition of ECMAScript was
formalising behaviour already common to implementations.

>>> It is allowed in ECMAScript v3, which has been around for
>>> over four years.


And has been a standard feature of browser scripting engine
implementations considerably longer.

>> I'd be happy to be wrong here and read about the required
>> productions from the ECMAScript 3 grammar in a posting of you.

>
> Will I do?
>
> Unless I'm missing something major (quite possible as I don't
> have this thread in full), you seem to be suggesting that
>
> function a() {
> function b() {
> }
> }
>
> is illegal. Is that correct? Well, in a code example, section
> 13.2 - Creating Function Objects, they have written almost
> precisely the above.


If nested functions were not explicitly supported there would not be
much point in ECMA 262 (3rd edition) going into quite so much detail
about how the scope chain and the internal [[Scope]] properties are
handled, as there would be no ECMAScript circumstances where it would
make any difference (which is probably why the second edition can get
away with defining only one form of scope chain for any execution
context).

> If you want the associated grammar:
>
> FunctionDeclaration :
> function Identifier ( FormalParameterListopt ) { FunctionBody }
>
> FunctionBody :
> SourceElements
>
> SourceElements :
> SourceElement
> SourceElements SourceElement
>
> SourceElement :
> Statement
> FunctionDeclaration


Yes, function bodies may explicitly contain function declarations, and
function expressions may appear anywhere that a MemberExpression can be
used:-

| 11.2 Left-Hand-Side Expressions
| Syntax
| MemberExpression :
| PrimaryExpression
| FunctionExpression
| MemberExpression [ Expression ]
| MemberExpression . Identifier
| new MemberExpression Arguments


> That suggests to me that it is perfectly legal to nest functions
> to any degree. I haven't checked to any great extent to see if
> the text notes limitations or exceptions, but I doubt there are
> any.
>
> One thing I had noticed in the grammar is that you may not place
> function declarations directly within a statement. As far as I
> can see, function statements may only occur in:
>
> - The program source at the "root" level.
> - Other functions (expressions or statements).
> - An eval() argument.
>
> That would make something like:
>
> if(...) {
> function myFunction() {
> }
> }
>
> illegal. However, a quick test shows that (at least some)
> browsers support it.


More involved tests would show extremely inconsistent handling of that
code. The production rules forbid a function declaration form appearing
within a block statement so the only valid ECMAScript interpretation of
that is as a function expression with optional identifier, and just
asserted (never assigned to anything or called, so a pointless
expression).

In practice browsers may take it as a function declaration (unless
explicitly parenthesised, which makes it unambiguously an expression)
and act on it during variable instantiation (effectively removing it
form its block context), and Mozilla browsers treat it as an expression
but erroneously (by ECMA 262) leak the optional identifier into the
containing scope (producing an effect indistinguishable form a
conditional function declaration (if such existed in ECMAScript).

> Why you'd do something like this, though, is another
> question.


You wouldn't, but an inner function expression, conditionally evaluated
and assigned, is completely normal.

Richard.


 
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Thomas 'PointedEars' Lahn
Guest
Posts: n/a
 
      10-18-2004
Richard Cornford wrote:

> Michael Winter wrote:
>> FunctionDeclaration :
>> function Identifier ( FormalParameterListopt ) { FunctionBody }
>>
>> FunctionBody :
>> SourceElements
>>
>> SourceElements :
>> SourceElement
>> SourceElements SourceElement
>>
>> SourceElement :
>> Statement
>> FunctionDeclaration

>
> Yes, function bodies may explicitly contain function declarations,


ACK, but only at first level.

> and function expressions may appear anywhere that a MemberExpression can
> be used:-
>
> | 11.2 Left-Hand-Side Expressions
> | Syntax
> | MemberExpression :
> | PrimaryExpression
> | FunctionExpression
> | MemberExpression [ Expression ]
> | MemberExpression . Identifier
> | new MemberExpression Arguments


However, the flaw of the latter argument (if that is what it is supposed
to be) is that a FunctionExpression is not a FunctionDeclaration and
vice-versa.


PointedEars
 
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Dr John Stockton
Guest
Posts: n/a
 
      10-18-2004
JRS: In article <(E-Mail Removed)>, dated Sun, 17 Oct
2004 23:26:27, seen in news:comp.lang.javascript, Thomas 'PointedEars'
Lahn <(E-Mail Removed)> posted :
>John G Harris wrote:
>
>> In article <(E-Mail Removed)>, Thomas 'PointedEars'
>> Lahn <(E-Mail Removed)> writes

>
>Please stop posting attribution novels; the reasons have been explained
>(to you) several times before.


They are invalid reasons. There is no support for them in accepted
Usenet standards and norms; and Usefor WIP allows a full attribution
such as I use.

You may recall that the German nation got rather a bad name in the early
1870s, the 1910s, and in 1933-45. It seems unwise of you to attempt to
repeat the situation single-handedly.

Given your rather silly habit of reviving ancient threads, threads that
the saner readers of c.l.j have long lost interest in, threads that are
no longer conveniently accessible to those using off-line newsreaders,
putting the date of the previous article in an attribution would be a
convenience to users of the group -- it is not always possible to
determine the date of a previous article from its message-ID in
References, and, when it is possible, many will not know how to do it,
and others find it inconvenient to understand.

In brief, pleas cease your Schickelgrubing.


>>> Nested functions are not allowed in ECMAScript and implementations.
>>> However, it is supported in JavaScript 1.5.

>>
>> It is allowed in ECMAScript v3, which has been around for over four
>> years.

>
>I'd be happy to be wrong here and read about the required productions
>from the ECMAScript 3 grammar in a posting of you.


They are supported in MSIE4, which Flanagan says is JS 1.2; that is over
six years old.


--
John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME
Web <URL:http://www.uwasa.fi/~ts/http/tsfaq.html> -> Timo Salmi: Usenet Q&A.
Web <URL:http://www.merlyn.demon.co.uk/news-use.htm> : about usage of News.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
 
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