AS3 RegEx returns null

Question

Can anyone explain why the code below traces null when on the timeline?

var cleanRegExp:RegExp = /^[a-zA-Z0-9]+(\b|\/)/;
var str:String = "/num83r5/and/letters/4/A/";
trace(str.match(cleanRegExp.toString()));

I've read the documentation, so I'm pretty sure that I'm declaring the RegEx correctly and that String.match() should only return null when no pattern is passed in, otherwise it should be an array with 0+ elements. I suspected a badly written expression, but surely that should still return an empty array?

EDIT: Both these trace "no matches" instead of either 5 or 0, depending on the expression being correct:

var cleanRegExp:RegExp = /^[a-zA-Z0-9]+(\b|\/)/;
var str:String = "/num83r5/and/letters/4/A/";
var res:Array = str.match(cleanRegExp);
trace((res == null) ? "no matches" : res.length);

And:

var cleanRegExp:RegExp = /^[a-zA-Z0-9]+(\b|\/)/;
var str:String = "/num83r5/and/letters/4/A/";
var res:Object = cleanRegExp.exec(str);
trace((res == null) ? "no matches" : res[0]);

It is a bug in the documentation, I've filed it here: bugs.adobe.com/jira/browse/FLEXDOCS-1363 — Borek Bernard
– Borek Bernard, Commented May 16, 2011 at 11:15

score 5 · Accepted Answer · 2011-04-18 12:16:47Z

5

UPDATE

If you're going to work in flash with regex, this tool is a must-have:

http://gskinner.com/RegExr/
http://gskinner.com/RegExr/desktop/

ORIGINAL ANSWER

Don't use toString(), you're then doing a literal search, which will include the addition of all of your regex formatting, including flags. Do:

str.match(cleanRegExp);

In fact the proper method is to reference the returned object like so:

var results:Array = str.match(cleanRegExp);

if(results != null){
     //We have a match!
}

edited Apr 18, 2011 at 12:16

answered Apr 18, 2011 at 11:59

user562566

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6 Comments

user562566 Over a year ago

Also I believe running the exec() command on the regex option is actually faster and it gives you more results data, instead of just an array of matches.

shanethehat Over a year ago

Can you look at the edit I posted? I removed toString(), but still get a null, which should only happen when no pattern is passed at all.

shanethehat Over a year ago

Same with exec(), Is there something obviously wrong with the expression?

user562566 Over a year ago

The flash docs are wrong. You get a NULL object if no match is made. I just tested your second example, it doesn't match because you have the ^ symbol which means it must be the start of the line, THEN a number or letter of any case. That doesn't exist in your example. Remove the hat, it works fine and traces the results.

user562566 Over a year ago

To answer your question yes there is something wrong with the format of the expressions. Code tested with corrected expressions works fine. Check my updated answer you need to install regexr and use it to write your regex its a live regex editor.

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