Regex - Why doesn't this pattern work when using the new RegExp method?

Question

I'm searching this string for an the 'invite=XXXX' part. I am using a capturing group to extract the value between '=' and ';'. When I use the first regex method it works, but when I use the second it doesn't. Why is this?

var string = "path=/; expires=Thu, 01 Jan 1970 00:00:00 GMT; invite=1323969929057; path=/; expires=Sat, 14 Jan 2012 17:25:29 GMT;";

// first method
var regex1 = /invite=(\w+)/;
var regexMatch1 = string.match(regex1);

// second method
var regex2 = new RegExp("/invite=(\w+)/");  
var regexMatch2 = string.match(regex2);

// log results
console.log(regexMatch1);
console.log(regexMatch2);

Working example here >>

Daniel A. White · Accepted Answer · 2011-12-15 17:52:08Z

2

You have to escape the \ and like Jake said, remove the slashes.

var regex2 = new RegExp("invite=(\\w+)");  
                                  ^ Notice 2 "\"

http://jsfiddle.net/ZqkQ9/10/

answered Dec 15, 2011 at 17:52

Daniel A. White

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1 Comment

wilsonpage Over a year ago

That is still logging 'null' in my console (Chrome)

Jake Feasel · Accepted Answer · 2011-12-15 17:52:57Z

2

When you use the RegExp() constructor, the slashes are not needed. Change to this:

var regex2 = new RegExp("invite=(\\w+)");

answered Dec 15, 2011 at 17:52

Jake Feasel

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1 Comment

Jake Feasel Over a year ago

You may also need to escape the backslash, as Daniel suggested

vcsjones · Accepted Answer · 2011-12-15 17:54:06Z

2

Because the / is for a regex literal. Since you are using the RegExp object, you need to remove the slashes. You also need to escape the backslash since you aren't using a literal:

var regex2 = new RegExp("invite=(\\w+)");  
var regexMatch2 = string.match(regex2);

answered Dec 15, 2011 at 17:54

vcsjones

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Comments

kubetz · Accepted Answer · 2011-12-15 17:54:23Z

2

It should be:

 var regex2 = new RegExp("invite=(\\w+)");

Regular expressions in string form have no / prefix and postfix and all escape characters must have \\ instead of \.

answered Dec 15, 2011 at 17:54

kubetz

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dheerosaur · Accepted Answer · 2011-12-16 09:12:34Z

1

You don't need the slashes while creating RegExp object using RegExp.

If you want, you can even compare the patterns using RegExp.source

Try console.log(regex1.source === regex2.source)

Reference: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/RegExp

edited Dec 16, 2011 at 9:12

answered Dec 15, 2011 at 17:55

dheerosaur

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falsarella · Accepted Answer · 2011-12-15 18:02:52Z

0

remove the /'s from the RegExp constructor, scape the \w and put the second parameter:

var regex2 = new RegExp("invite=(\\w+)", "");

answered Dec 15, 2011 at 18:02

falsarella

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