A Question About RegExp in Javascript

Question

I wrote a regular expression
^([+/-]?([0-9]+(.)?)|([0-9]*.[0-9]+))$
I create it by two ways

var _regex = "^([+/-]?([0-9]+(\.)?)|([0-9]*\.[0-9]+))$";
var _regexFloat = new RegExp(_regex);

and

var _regexFloat = /^([+/-]?([0-9]+(\.)?)|([0-9]*\.[0-9]+))$/ ;

the testing data is "1a" and "a1".
at the second way, it work fine.
but in the first way, it returns true.

Can anyone suggest me if I have something wrong.

Thanks very much.

Environment:

Windows Server 2003
IE 6

Hello, what is this regex for ? Is it to know if a string contains a float ? — Fabien Ménager
– Fabien Ménager, Commented Jun 22, 2009 at 6:37

Jeff Meatball Yang · Accepted Answer · 2009-06-22 06:37:26Z

5

I believe you'll need to escape those backslashes in the string (in the first version).

Try this:

var _regex = "^([+/-]?([0-9]+(\\.)?)|([0-9]*\\.[0-9]+))$";
var _regexFloat = new RegExp(_regex);

answered Jun 22, 2009 at 6:37

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2 Comments

Of course this is exactly why the second syntax exists. Escaping makes it less readable.

I agree, I use the second version.