What's wrong with my Javascript regex?

Question

I would like regex to match if and only if the string is none, family or work (but not my family, for example).

Why the following code results with "match" ? Why ^ and $ do not work ?

var regex = new RegExp("^none|family|work$");
var str = "my family";
document.write(regex.test(str) ? "match" : "no");

Marcelo Cantos · Accepted Answer · 2010-08-23 11:50:05Z

4

The | operator has low precedence, so you effectively have (^none)|(family)|(work$), which matches anything beginning with none, containing family or ending with work.

Use this instead:

^(none|family|work)$

answered Aug 23, 2010 at 11:50

Marcelo Cantos

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Timwi · Accepted Answer · 2010-08-23 11:51:31Z

4

Your regex matches either:

“none” at the beginning of the string;
“family” anywhere in the string; or
“work” at the end of the string.

What you probably want instead is

var regex = new RegExp("^(none|family|work)$");

answered Aug 23, 2010 at 11:51

Timwi

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