Problem with regex lookahead in javascript

Question

I'm trying to match only when all space-separated words are longer than 3 word characters (3 word characters are mandatory, abc* is right but ab* is not). This is my test:

<html>
        <body>
                <script>
                var re = /(?!(\W|^)\w{0,2}(\W|$)).*/i;
                var texts = new Array("ab","ab*","abc de*", "ab* def");
                for (textindex in texts)
                {
                        var text = texts[textindex];
                        var matched = re.test(text);
                        document.write(matched + "<br/>")
                }
                </script>
        </body>
</html>

All texts match, but I believe that none should match. Maybe I'm misunderstanding some fundamental on how lookahead works.

score 3 · Accepted Answer · 2011-06-29 17:47:40Z

3

The simple regex to test that would be:

/^(\s?\S{3,})+$/

As for why your regex isn't working, your negative look-ahead simply means "this does not exist at this exact point", so no matter what your input is you'll get a match at the end of the line at the very least.

edited Jun 29, 2011 at 17:47

answered Jun 29, 2011 at 17:40

user578895

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4 Comments

Doppelganger Over a year ago

But that one doesn't match "abc*" or "abcd* def*" and both should match.

Doppelganger Over a year ago

Ok, I added \S* at the end, and at least that matched all my test patterns. Thanks! So the final answer should be: /^(\s?\w{3,}\S*)+$/

Doppelganger Over a year ago

\w was right, I needed 3 forced word characters, and THEN any nonspace (asterisk, in my examples). "ab*" shouldn't match. (maybe this wasn't clear in the original question, I'll clarify this point.

Doppelganger Over a year ago

I find your explanation of my lookahead not working interesting, but I don't get it. If the lookaheads always match at the end of the line, I don't see how do you get one that works. Could you please ellaborate ?

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