Exact matching using regexp

Question

var name ='John Rock';
alert((/^John|Steve$/i).test(name));

http://jsfiddle.net/czBhb/

This code alerts true, because doesn't use an exact mathing, but has to.

Should return true for John and joHn (case matching off). But not for John 12 or mahjohng.

There is | in the code, we should keep it.

How do I fix this regexp?

Possible duplicate of [Regex - Match whole string](http://stackoverflow.com/q/6298566/851811). — Xavi López, Feb 25 '13 at 13:37
Apparently `|` has lower operator precedence than `^` and `$`, which is a little counterintuitive. So you need to wrap `John|Steve` in parentheses, in order to apply the `|` before the `^` and `$` anchors. — mellamokb, Feb 25 '13 at 13:38
I already pointed out how to do this in [my answer to your earlier question](http://stackoverflow.com/a/15066690/157247) more than half an hour ago, as soon as Beat Richartz pointed out the problem. — T.J. Crowder, Feb 25 '13 at 13:39

score 3 · Answer 1 · edited May 23 '17 at 12:03

3

If your goal is to match exactly John or Steve, you want to put a group in there:

alert(/^(?:John|Steve)$/i.text(name));

Also note the i for case insensitivity. (I did point this out in my answer to your other question more than half an hour ago, as soon as Beat Richartz pointed out the problem.)

edited May 23 '17 at 12:03

Community

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answered Feb 25 '13 at 13:37

T.J. Crowder

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score 2 · Accepted Answer · answered Feb 25 '13 at 13:37

2

What about

var name ='John Rock';
alert((/^(John|Steve)$/i).test(name));

answered Feb 25 '13 at 13:37

Udo Klein

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score 2 · Answer 3 · answered Feb 25 '13 at 13:37

2

Try this:

alert(/^(?:John|Steve)$/i).test(name))

(?: groups between ^ and $ without actually creating the group

/i for the case insensitivity

answered Feb 25 '13 at 13:37

Beat Richartz

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score 1 · Answer 4 · answered Feb 25 '13 at 13:40

The point is in the ^ and $ delimiters. As already pointed out in the comments, they seem to have precedence over the OR, so your regex is matching anything that starts with John, or ends with Steve.

Put the delimiters outside the OR:

var name ='John Rock';
alert((/^(John|Steve)$/).test(name));

Exact matching using regexp

4 Answers4