Trouble with JavaScript regex code to match characters and numbers

Question

I would like help with solving a problem using regular expressions.

I've written the following JavaScript code:

var s = '/Date(1341118800000)/';
var regex = new RegExp('^/Date\(\d+\)/$');
if ( typeof s === 'string' && s.match(regex) )
    s = 'abc';
alert (s);

I have written a regex that I want to match strings that begin with the following exact characters: /Date( followed by one or more digits, followed by the exact characters )/ and nothing more.

In the above JavaScript code, I expect that the string 'abc' should be assigned to s, but at the conclusion of this code, the value of s is '/Date(1341118800000)/'.

How can I fix this?

In this case, if the string s matches the regular expression, the string 'abc' should be assigned to s. — Vivian River
– Vivian River, Commented Jul 27, 2012 at 18:50
Why not just s = '/Date(1341118800000)/' == s ? "abc" : s; — Larry Battle
– Larry Battle, Commented Jul 27, 2012 at 19:08

pimvdb · Accepted Answer · 2012-07-27 18:50:24Z

1

The escape slashes are already consumed by the string, i.e. "\(" === "(". The resulting unescaped string is passed to new RegExp, which interprets ( as a special character.

You should use a regular expression literal and escape the /s as well:

var regex = /^\/Date\(\d+\)\/$/;

To test whether a string matches, you can use:

regex.test(s);

answered Jul 27, 2012 at 18:50

pimvdb

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2 Comments

Vivian River Over a year ago

I tried your fix and it seems to work. However, I was following a "cheat sheet" here: addedbytes.com/download/regular-expressions-cheat-sheet-v2/png. The "cheat sheet" does not include / as a character that should be escaped. Is that an error on the cheat sheet, or is it specific to regex in JavaScript that / must be escaped?

pimvdb Over a year ago

@Daniel Allen Langdon: Is that sheet JavaScript specific? In JavaScript, regexp literals are enclosed by /, so you need to escape them if you want to use them literally. (The sheet also e.g. says > needs escaping but it doesn't in JavaScript.)

Larry Battle · Accepted Answer · 2012-07-27 19:00:15Z

0

The problem is that "/^/Date$\d+$/$/" converts to "/^/Date(d+)/$/" in javascript.

"/^/Date$\d+$/$/" == "/^/Date(d+)/$/" // returns true

So just escape the backspace, \, to fix the problem.

var regex = new RegExp('^/Date\$\\d+\$/$');

edited Jul 27, 2012 at 19:00

answered Jul 27, 2012 at 18:51

Larry Battle

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Comments

Ωmega · Accepted Answer · 2012-07-27 19:02:59Z

0

I believe you are looking for this code:

var s = '/Date(1341118800000)/';
s = s.match(/^\/Date\((\d+)\)\/$/)[1];
alert(s);

Test it here.

answered Jul 27, 2012 at 19:02

Ωmega

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