How to Properly Format a Regex in JavaScript

Question

Trying to pull the version off of the Chrome user agent which is formatted like "Chrome/34.0.1847.116".

This is working:

userAgent.match(/.*Chrome.*?([\d|\.]*)\s/i);

This is not working (and I'm trying to get it working):

var versionRegularExpression = new RegExp('.*'+'Chrome'+'.*?([\d|\.]*)\s', 'i');
userAgent.match(versionRegularExpression);

I must be formatting my new RegExp incorrectly - can anyone tell me how I am messing up?

The full user agent is:

var userAgent = 'Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/34.0.1847.116 Safari/537.36';

score 4 · Answer 1 · edited Jun 20 '20 at 09:12

4

When you use RegExp object instead of RegEx literal, you need to escape the \ as well,

new RegExp('.*'+'Chrome'+'.*?([\\d|\\.]*)\\s', 'i');

Also, Chrome doesn't need to be concatenated, it can be part of the single string literal, like this

new RegExp('.*Chrome.*?([\\d|\\.]*)\\s', 'i');

As Paulpro points out in the comments section, when you use character classes, | will be taken as one of the characters allowed, not the OR operator. So, you don't need it there

new RegExp('.*Chrome.*?([\\d\\.]*)\\s', 'i');

Quoting from MDN's RegExp page,

When using the constructor function, the normal string escape rules (preceding special characters with \ when included in a string) are necessary. For example, the following are equivalent:
var re = /\w+/;
var re = new RegExp("\\w+");

edited Jun 20 '20 at 09:12

Community

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answered Apr 15 '14 at 04:02

thefourtheye

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Awesome! Will accept this answer. Super helpful to know I needed the extra escaping slash. – Kirk Ouimet Apr 15 '14 at 04:04
Downvoter, please let me know what is wrong. – thefourtheye Apr 15 '14 at 04:04
@thefourtheye I downvoted, because I misunderstood the second sentence in your answer. Removed the downvote, but I still think the character class `[\d|\.]` is unusual, since it matches `|` characters for no real reason, so no upvote yet. – Paul Apr 15 '14 at 04:07
It doesn't really have anything to do with the "RegExp object" (I assume you mean constructor). It has to do with using string literal syntax, which also uses the backslash as the opening of an escape sequence. – cookie monster Apr 15 '14 at 04:08
@Paulpro You are correct :) I included that information in the answer. – thefourtheye Apr 15 '14 at 04:09
@thefourtheye Nice, +1 – Paul Apr 15 '14 at 04:12
@cookiemonster Yes, I clarified that in the answer. – thefourtheye Apr 15 '14 at 04:14

score 2 · Answer 2 · answered Apr 15 '14 at 04:11

2

There seems to be no point on matching .* before of after Chrome. You also do not need a | or to escape the . in a character class. I would use this:

userAgent.match(/Chrome\/([\d.]*)/);

answered Apr 15 '14 at 04:11

Paul

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How to Properly Format a Regex in JavaScript

2 Answers2