JavaScript Regex does not match exact string

Question

In the example below the output is true. It cookie and it also matches cookie14214 I'm guessing it's because cookie is in the string cookie14214. How do I hone-in this match to only get cookie?

var patt1=new RegExp(/(biscuit|cookie)/i);
document.write(patt1.test("cookie14214"));

Is this the best solution?

var patt1=new RegExp(/(^biscuit$|^cookie$)/i);

newfurniturey · Accepted Answer · 2012-08-22T19:30:17.577

6

The answer depends on your allowance of characters surrounding the word cookie. If the word is to appear strictly on a line by itself, then:

var patt1=new RegExp(/^(biscuit|cookie)$/i);

If you want to allow symbols (spaces, ., ,, etc), but not alphanumeric values, try something like:

var patt1=new RegExp(/(?:^|[^\w])(biscuit|cookie)(?:[^\w]|$)/i);

Second regex, explained:

(?:                 # non-matching group
    ^               # beginning-of-string
    | [^\w]         # OR, non-alphanumeric characters
)

(biscuit|cookie)    # match desired text/words

(?:                 # non-matching group
    [^\w]           # non-alphanumeric characters
    | $              # OR, end-of-string
)

edited Aug 22 '12 at 19:30

answered Aug 22 '12 at 19:15

newfurniturey

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have you tested this? i dont think you can use the negative lookahead after the desired string. – jbabey Aug 22 '12 at 19:36
@jbabey Yeah, tested with firebug; also, the regexes are not using any lookaheads (positive, or negative). The second one is using a non-matching group, `(?:`, if that's what you're confusing with `(?!` – newfurniturey Aug 22 '12 at 19:39
@jbabey It's a good one to use; it works like it's name implies - the regex has to match that group also, but it doesn't return it in the list of matches. So, the return-array would only contain two groups (first is the "full context" of the match, second is the matched word). – newfurniturey Aug 22 '12 at 19:44

score 2 · Answer 2 · answered Aug 22 '12 at 19:14

Yes, or use word boundaries. Note that this will match great cookies but not greatcookies.

var patt1=new RegExp(/(\bbiscuit\b|\bcookie\b)/i);

If you want to match the exact string cookie, then you don't even need regular expressions, just use ==, since /^cookie$/i.test(s) is basically the same as s.toLowerCase() == "cookie".

JavaScript Regex does not match exact string

2 Answers2