How to translate ruby regex to javascript? - (?i-mx:..) and Rails 3.0.3

Question

Im using validates_format_of method to check email format:

validates_format_of :email, :with => /^([^@\\s]+)@((?:[-a-z0-9]+\\.)+[a-z]{2,})$/i

Answer 1

Ruby and JavaScript regular expressions are parsed and executed by different engines with different capabilities. Because of this, Ruby and JavaScript regular expressions have small, subtle differences which are slightly incompatible. If you are mindful that they don't directly translate, you can still represent simple Ruby regular expressions in JavaScript.

Here's what client side validations does:

class Regexp
  def to_javascript
    Regexp.new(inspect.sub('\\A','^').sub('\\Z','$').sub('\\z','$').sub(/^\//,'').sub(/\/[a-z]*$/,'').gsub(/\(\?#.+\)/, '').gsub(/\(\?-\w+:/,'('), self.options).inspect
  end
end

The recent addition of the routes inspector to rails takes a similar approach, perhaps even better as it avoids monkey patching:

def json_regexp(regexp)
  str = regexp.inspect.
        sub('\\A' , '^').
        sub('\\Z' , '$').
        sub('\\z' , '$').
        sub(/^\// , '').
        sub(/\/[a-z]*$/ , '').
        gsub(/\(\?#.+\)/ , '').
        gsub(/\(\?-\w+:/ , '(').
        gsub(/\s/ , '')
  Regexp.new(str).source
end

Then to insert these into your javascript code, use something like:

var regexp = #{/^([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})$/i.to_javascript};

Answer 2

I've written a small gem that translates Ruby regexes to JavaScript:

https://github.com/janosch-x/js_regex

It can handle more cases than the gsub approach, and includes warnings if any incompatibilities remain.

Note that, whatever you do, not all Ruby regexes can be fully translated to JS, because Ruby's regex engine has a lot of features that JavaScript's doesn't have.

Answer 3

The reason is that you are converting your regular expression using .to_s instead of .inspect. What you need to do in your view is use .inspect to get the proper format. Here is some sample code that should explain the issue:

email = /^([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})$/i
email.to_s #"(?i-mx:^([^@\\s]+)@((?:[-a-z0-9]+\\.)+[a-z]{2,})$)"
email.inspect #"/^([^@\\s]+)@((?:[-a-z0-9]+\\.)+[a-z]{2,})$/i"

so, in your javascript view do something like this to get the actual string representation you want:

<%= email.inspect %>