regular expression (?:x)

[muazzez]

You will use (?: x)
Can you write a short code? Thanks...

(?: x) kullanarak, kısa bir kod yazabilir misin?

[MikeFoster]

Hi muazzez,

That is the Conditional Operator. For example...

// Given...
var x, a = 1;
// then...
x = (a == 2) ? 10 : 20;
// is the same as...
if (a == 2) {
  x = 10;
}
else {
  x = 20;
}

// In general...
x = (expression1) ? expression2 : expression3;
// is the same as...
if (expression1) {
  x = expression2;
}
else {
  x = expression3;
}

[Logic Ali]

Hi muazzez,

That is the Conditional Operator.

I think he's referring to non-capturing parentheses.

Looks like a homework question.

[Mittineague]

I have never used it in javascript regex, but in PHP PCRE (Perl compatible) it is a non-capturing subpattern. AFAIK javascript regex is based on Perl regex so I imagine it has the same use in javascript. From the PHP docs http://us.php.net/manual/en/referenc...ern.syntax.php

The fact that plain parentheses fulfil two functions is not always helpful. There are often times when a grouping subpattern is required without a capturing requirement. If an opening parenthesis is followed by "?:", the subpattern does not do any capturing, and is not counted when computing the number of any subsequent capturing subpatterns.

@muazzez What you posted is "a short code"

[felgall]

I can confirm that it is a non-capturing sub-pattern.
See http://javascript.about.com/library/blre16.htm for more info.


Javascript supports most of the same regular expression options as PERL etc but there are a few that it doesn't support due to the way that it processes regular expressions.

[7stud]

str1 = "abHELLO-HELLO-GOODBYE_GOODBYE_HI-HI-cd"
str2 = "abGOODBYE_cd"
re = /(ab)(?:HELLO-)*(?:GOODBYE_)*(?:HI-)*(cd)/

m1 = str1.match(re)
m2 = str2.match(re)
alert(m1[1] + m1[2])    //abcd
alert(m2[1] + m2[2])    //abcd

[muazzez]

Thanks.. Now I can write.

  
<script type="text/javascript">

var x = "bu bir deneme";
var dizi;
if ( dizi = x.match(/(bu)\s(?:bir)\s(deneme)/i) ) {
   document.write("$1: " + dizi[1]+"<br>$2: " + dizi[2]);
}

</script>

[MikeFoster]

Thanks guys. I didn't know about that

[7stud]

Thanks.. Now I can write.

  
<script type="text/javascript">

var x = "bu bir deneme";
var dizi;
if ( dizi = x.match(/(bu)\s(?:bir)\s(deneme)/i) ) {
   document.write("$1: " + dizi[1]+"<br>$2: " + dizi[2]);
}

</script>

That is a superfluous use of (?: ). You could accomplish the same thing by eliminating the grouping:

/(bu)\sbir\s(deneme)/i

(?: ) is used when you need to apply a modifier to a group, but you don't want the parentheses you use to create a numbered group in your match. Look at the example in my previous post and note how the (?: ) groupings require a modifier in order to get the proper match.

[SimplyFu]

wow I rarely use non-capturing in many cases, thanks for this tips

[SimplyFu]

I just try this but couldn't figure out how can I escape a character in the non capturing pattern?

"234234p".match(/\d+(?!.)/)  => should not match, but it is

// second try
"234234.".match(/\d+(?!\.)/)  => match 234234  // is that right?

[Mittineague]

Do you mean for the character after the question mark to be a colon ":" or the exclamation point "!"

[7stud]

"234234p".match(/\d+(?!.)/) => should not match, but it is

...should not match, and it doesn't:

if("234234p".match(/\d+(?!.)/) )
	alert("yes")
else
	alert("no")

//output: no

[SimplyFu]

\d+(?!.) is a non capturing with a sequence of digits without followed by a dot character. Well, I found out it was a typo, 7stud is right. it works well. Thanks