Regular Expression Mystery

[dhannotte]

I like to code parameters to my Javascript functions within strings
that look like UNIX command parameters. For instance I might say

myfunc("-center -w:100% -nocache");

I've written a function to extract the value of any one flag or
keyword:value pair, but it's not working. To continue with the example,
I call

get_value(values_passed, "-w:80%");

which means that 'values_passed' is the string that was passed to me,
'-w:' is the keyword I'm interested in and '80%' is its default value.
Here is the function I wrote:

function get_value(parms, key_and_val)
{
var colon = key_and_val.indexOf(':');
var key = key_and_val.substr(0, colon);
var val = key_and_val.substr(colon + 1);
var regex = new RegExp(key + ":(.*)[ $]"); // IS THIS CORRECT?
var rslt = regex.exec(parms);

var result;
if (rslt == null)
{
result = val; // Use default value
}
else
{
result = rslt[0];
}
return result;
}

'rslt' is always null. I've even tried using match() instead of exec():

var rslt = parms.match(regexp);

and that results in 'null' too. Can anyone think of anything I can try
to learn out what's wrong here? Does my regexp violate some syntax rule
I'm unaware of, for instance? Thanks very, very much.

Dean Hannotte
http://www.hannotte.net

[RobG]

dhannotte wrote:

I like to code parameters to my Javascript functions within strings
that look like UNIX command parameters. For instance I might say

myfunc("-center -w:100% -nocache");

I've written a function to extract the value of any one flag or
keyword:value pair, but it's not working. To continue with the example,
'not working' is a pretty useless description of your problem :-(

You need to specify what you expect to get and what you actually get,
then explain how they are different, even if it seems pretty obvious to
you. It's much more reliable to have readers skip a bit of wordiness
than have to guess at missing explanations.

I call

get_value(values_passed, "-w:80%");

which means that 'values_passed' is the string that was passed to me,
'-w:' is the keyword I'm interested in and '80%' is its default value.
Here is the function I wrote:

function get_value(parms, key_and_val)
{
var colon = key_and_val.indexOf(':');
var key = key_and_val.substr(0, colon);
var val = key_and_val.substr(colon + 1);
Here's a couple of suggestions that make no difference to the output, so
whether you use them or not is up to you:

var kv_bits = key_and_val.split(':');
var key = kv_bits[0];
var val = kv_bits[1] || '' ;
var regex = new RegExp(key + ":(.*)[ $]"); // IS THIS CORRECT?
It depends on what you are after, see below.

var rslt = regex.exec(parms);

var result;
if (rslt == null) ----------^^^^^^^^^^^^
Note A.

Be careful. If '-w:' is passed as a parameter, then rslt is not null
and rslt[1] will be an empty string ''. Consider:

if (rslt == null || !rslt[1] || rslt[1] == '' )

{
result = val; // Use default value
}
else
{
result = rslt[0]; -----------------------^^^
Note B.

}
return result;
}

'rslt' is always null.
Running get_value() as posted and calling it with:

alert( get_value("-center -w:100% -nocache", "-w:80%") );
In both Firefox and IE '-w:100%' is displayed. Is that 'working' or
not? If -w:100% is changed to -w, then '80%' is displayed. Does that
mean the first result should be '100%'? If so, then change B above to:

result = rslt[1];

'rslt' is always null.

Not for me. Why not have the parameter string entered with spaces
between flags and values, then you can just use split and parse the
resulting array.

e.g.

parseParms("-center -w 100% -nocache")

function parseParms(parms)
{
parms = parms.split(/\s+/);
var parm, val, i=parms.length;

while ( (parm = parms.shift()) ){
if ( --i && parms[0].substring(0,1) != '-' ){
val = parms.shift();
--i;
} else {
val = '';
}

// Do something with parameter & value
alert('Parm: ' + parm + '\nValue: ' + val);
}
}
--
Rob

[Dr John Stockton]

JRS: In article <11**********************@p10g2000cwp.googlegroups .com>
, dated Thu, 9 Mar 2006 15:26:19 remote, seen in
news:comp.lang.javascript, dhannotte <dh****@nyc.rr.com> posted :

I like to code parameters to my Javascript functions within strings
that look like UNIX command parameters. For instance I might say

myfunc("-center -w:100% -nocache");

That's weird.

IMHO you'd do better to pass an Object (literal or variable)

myfunc({center:true, w:"100%", cache:false})

You don't have to provide all possible values :

function myfunc(A) { var Ht = A.h | 0, ... ; ... }

You'd be able to use 1 & 0 as synonyms for true and false

Javascript should be written using javascript idioms, not those of a
UNIX command shell.

Strings should be used only for material which is intrinsically textual
(except sometimes).

--
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