Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.javascript > #13345

Re: How to Pass variable name to a function

Show key headers only | View raw

Thomas 'PointedEars' Lahn wrote:
> 
> Stan Weiss wrote:
> 
> > I have this code in a form which calls the save function.
> >
> > <TR><TD ALIGN="RIGHT">
> > <b>Valve Diameter in Millimetres </b>
> > </TD><TD>
> > <INPUT TYPE="text" NAME="VD" SIZE=7  onChange="save(stanForm.VD.value,
> > AInput, 'Valve Diameter')">
> > </TD></TR>
> >
> > function save( field, vary, text ) {
> >      if( isNaN( field ) )
> >      {
> >         alert( text + " is not numeric" );
> >      }
> >      else
> >      {
> >          AInput = eval(field);  // this Works
> >          vary = eval(field);    // this does not workWorks
> >      }
> > }
> >
> > Can anyone see what I am doing wrong?
> 
> Yes; it is (at least) the following:
> 
> 1. Your referencing is proprietary, at best error-prone, needlessly.
> 
>      stanForm.VD.value
> 
>    is not appropriate referencing (throw that book away).  Assuming that
>    your control is descendant of a form element named `stanForm' (which you
>    have not showed), an appropriate, standards-compliant, backwards
>    compatible and less error-prone referencing would be
> 
>      document.forms['stanForm'].elements['VD'].value
> 
>    However, as that code appears to be part of the event-handler attribute
>    value of the very element that is represented by
> 
>      document.forms['stanForm'].elements['VD']
> 
>    you can replace that with
> 
>      this
> 
>    so that the element reads
> 
>      <input type="text" name="VD" size="7"
>             onchange="save(this.value, AInput, 'Valve Diameter')">
> 
> 2. You are referring to an identifier before you declare or define it.
>    `AInput' is neither declared nor defined before save() is called, so for
>    all we know,
> 
>      save(this.value, AInput, 'Valve Diameter')
> 
>    throws a ReferenceError when evaluating `AInput'.  Check your error
>    console.
> 
>    It is possible that you have
> 
>      var AInput;
> 
>    somewhere in your code, or even
> 
>      <form name="stanForm" …>
>        …
>        <input name="AInput" …>
>        …
>      </form>
> 
>    (see also <http://stackoverflow.com/questions/9158238/why-js-function-
>     name-conflicts-with-element-id/9160009#9160009>), but then you should
>    have posted that.
> 
> 3. You are using eval().
> 
>    Given the aforementioned `forms' and `elements' collections, you do not
>    have to use eval() here.  See also <http://jibbering.com/faq/#eval> (in
>    general, *always* read the FAQ of the newsgroup(s) *before* you post to
>    them).
> 
> 4. You are using eval() wrong.
> 
>    You are passing for the argument of eval() – `field' – the value of the
>    control that calls the very same function.  One could surmise from this
>    that you might be trying to implement a calculator.
> 
>    However, this assumption contradicts your programming where you
>    explicitly do not enter the branch with the eval() calls when the string
>    value cannot be interpreted as a number, such as a non-trivial equation
>    (operand operator operand).
> 
>    It is also rather far-fetched to assume that your user would enter
>    the names of controls in your form in that input control.
> 
>    Therefore, your calls to eval() appear to be completely pointless.  To
>    convert a string value to a number value, use the unary `+' operator,
>    or the parseInt(…, radix) or parseFloat(…) function calls.
> 
> 5. "Does not work" is not a problem description.  Read the FAQ on how to
>    post when you desire useful answers.
> 
> 6. You can assign to a function argument, but that does not change the
>    value passed for that argument.  There is no call-by-reference, all
>    function arguments are values.  (But it does not appear as if you were
>    trying to use the assumed assigned value anywhere, so this appears
>    to be pointless anyway.)
> 
> 7. The `change' event occurs on the control when the control loses focus,
>    not before.  Do not have your users rely on that, provide a button for
>    the computation.  You may perform form validation on change, but you
>    should do it in a non-obtrusive way (like adding color).
>    Perform any validation that hinders or blocks the user's workflow (like
>    an alert message) only on submit; the `form' element has an `onsubmit'
>    event-handler attribute for that.
> 
> 8. Avoid the window.alert() method.  In particular, in recent Gecko-based
>    browsers, such an alert message disables the entire viewport of a tab
>    until the message is dismissed, and it is very likely to cover the parts
>    where the error is.  (IMHO yet another incredibly bad design decision
>    in Geckos that we now need to work around – thanks guys :->)
> 
> 9. Is your markup Valid?  Declare HTML 4.01 Strict or (if necessary) HTML5,
>    and replace presentational attributes (like `align') and elements with
>    CSS.  <http://validator.w3.org/>
> 
> Bottom line: Learn the markup and programming languages before you use an
> API with the programming language, and try something much more simple than
> this first.
> 
> PointedEars
> --
> Anyone who slaps a 'this page is best viewed with Browser X' label on
> a Web page appears to be yearning for the bad old days, before the Web,
> when you had very little chance of reading a document written on another
> computer, another word processor, or another network. -- Tim Berners-Lee

Is this a moderated group?
Are you the group moderator?

I poster enough code to get the answer I needed. While you seem to want
to make all kinds of ASSumptions about things that were not posted.

Thanks for looking

Stan

PS Some old habits - presentational attributes (like `align') go back to
when I used to do this back in 1997. You know what people tell me that
those old scripts still work great.

Back to comp.lang.javascript | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-11 12:26 -0400
  Re: How to Pass variable name to a function Andreas Bergmaier <andber93@web.de> - 2012-04-11 19:47 +0200
    Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-11 14:21 -0400
      Re: How to Pass variable name to a function Stefan Weiss <krewecherl@gmail.com> - 2012-04-11 20:53 +0200
        Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-11 15:16 -0400
          Re: How to Pass variable name to a function Gene Wirchenko <genew@ocis.net> - 2012-04-11 15:18 -0700
  Re: How to Pass variable name to a function "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-04-11 21:20 +0000
  Re: How to Pass variable name to a function Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-04-11 23:56 +0200
    Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-12 00:48 -0400
      Re: How to Pass variable name to a function Andrew Poulos <ap_prog@hotmail.com> - 2012-04-12 15:21 +1000
        Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-12 02:11 -0400
          Re: How to Pass variable name to a function Andrew Poulos <ap_prog@hotmail.com> - 2012-04-12 18:57 +1000
            Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-12 09:35 -0400
      Re: How to Pass variable name to a function Stefan Weiss <krewecherl@gmail.com> - 2012-04-12 08:08 +0200
        Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-12 10:13 -0400
      Re: How to Pass variable name to a function Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-04-12 22:47 +0200
        Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-12 17:04 -0400
          Re: How to Pass variable name to a function Tim Streater <timstreater@greenbee.net> - 2012-04-12 22:17 +0100
          Re: How to Pass variable name to a function Scott Sauyet <scott.sauyet@gmail.com> - 2012-04-13 05:13 -0700
            Re: How to Pass variable name to a function "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-04-13 16:27 +0000
              Re: How to Pass variable name to a function Scott Sauyet <scott.sauyet@gmail.com> - 2012-04-16 04:11 -0700
        Re: How to Pass variable name to a function "Tom de Neef" <tdeneef@qolor.nl> - 2012-04-12 23:34 +0200
          Re: How to Pass variable name to a function Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-04-13 10:03 +0200
          Re: How to Pass variable name to a function Erwin Moller <erwinmollerusenet@xs4all.nl> - 2012-04-13 12:03 +0200
            Re: How to Pass variable name to a function Andrew Poulos <ap_prog@hotmail.com> - 2012-04-13 21:35 +1000
            Re: How to Pass variable name to a function Gene Wirchenko <genew@ocis.net> - 2012-04-13 09:00 -0700
  Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-12 14:03 -0400
  Re: How to Pass variable name to a function Dr J R Stockton <reply1215@merlyn.demon.co.uk.not.invalid> - 2012-04-12 20:06 +0100
    Re: How to Pass variable name to a function Stan Weiss <srweiss@erols.com> - 2012-04-12 18:54 -0400

csiph-web