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Message-ID: <2271012.FRqVoOGUtd@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
Organization: PointedEars Software (PES)
Date: Sat, 25 Feb 2012 00:33:41 +0100
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Subject: Re: Cant use <input text as a numeric
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Cal Who wrote:

> "Denis McMahon" wrote:
>> On Fri, 24 Feb 2012 16:54:55 -0500,  Cal Who wrote:
>>> <input  type="text" value="60"  name="timeTotal" />
>>
>>> [can't use] document.ScrabbleStopWatch.timeTotal as a numeral.
>>
>> This refers to the field.
>>
>>> What am I doing  wrong??

You are attempting to convert an object to a number that has no built-in 
numeric representation.  The parseFloat() function/method converts its 
argument to String (if necessary) before it parses it to a Number value 
(ECMAScript Language Specification, 5.1 Edition, section 15.1.2.3).  
Conversion to string may call (through ToPrimitive() and [[DefaultValue]]) 
an object's toString() method or valueOf() method, whichever can be found 
first (ibid., section 9.8).

If a host object like a DOM object inherits from Object.prototype, then it 
inherits Object.prototype.toString(), which is specified to return "[object 
$CLASS]", where $CLASS is the value of the internal [[Class]] property of 
the object.  In this case, in most cases the value of the [[Class]] property 
will be the identifier of the W3C DOM interface that the object implements, 
so "HTMLInputElement" here.  And "[object HTMLInputElement]" cannot be 
parsed into a Number value by parseFloat().  Likewise, in the MSHTML DOM the 
string representation of a host object may be "[object]", for which the same 
applies.

>> The string value of the field named "timeTotal" in the form named
>> "ScrabbleStopWatch" might be read using:
>>
>> var strval = document.ScrabbleStopWatch.timeTotal.value;
> Thanks, that did it!

However, the proper way to refer to the value of the control is

  document.forms["ScrabbleStopWatch"].elements["timeTotal"].value

whereas

  document.forms["ScrabbleStopWatch"]

can be replaced with a shorter reference, such as `this' in an event-handler 
attribute value of the `form' element in question, and `this.form' in an 
event-handler attribute of the control in question; respectively, `o.form' 
in a function called from the latter event-handler attribute, if `o' is a 
function argument for which `this' is passed from the calling context.

<https://developer.mozilla.org/en/DOM/document#Properties> pp.

>> and to take this as a floatVal:
>>
>> numv = floatVal(document.ScrabbleStopWatch.timeTotal.value);
> Is floatVal exactly the same as parseFloat?
> I notice you used parseFloat below.

There is no built-in floatVal() function in any sufficiently distributed 
ECMAScript implementation.  There is a floatval() function in PHP which but 
does the same as parseFloat() in ECMAScript implementations.

<https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/parseFloat>
<http://php.net/floatval>

>> But the more common way these days is to not use a form if you're not
>> actually submitting the form data in a request, rather assign each field
>> an id value and:
> Do you neam - not use a <form> at all unless there is an element that
> causes a form submit like --- for example, what?

A `form' element can be useful for referring to other controls even if the 
form is never submitted.  However, using a `form' element enables control's 
values to be submitted even if client-side scripting is unavailable.

You would be well-advised not to learn from wannabes like Dennis McMahon, 
unless you would want to learn by bad example.


PointedEars
-- 
When all you know is jQuery, every problem looks $(olvable).