Regular expression stored in a variable not working when matching

Question

I have a hash of "allowed links" to render on my rails backend, something like this

    ALLOWED_URLS = {
      "vimeo": {
          :regex => "/https?:\/\/(?:www\.|player\.)?vimeo.com\/(?:channels\/(?:\w+\/)?|groups\/([^\/]*)\/videos\/|album\/(\d+)\/video\/|video\/|)(\d+)(?:$|\/|\?)/",
},
      "youtube": {
          :regex => "/^.*(youtu.be\/|v\/|u\/\w\/|embed\/|watch\?v=|\&v=)([^#\&\?]*).*/",
    }

In each of the stored values, I have a regular expression to try if a link is from youtube or Vimeo and the video id I have tried them both and they work perfectly.

But when I pass that variable to my CoffeeScript and convert it to a JSON, the regex does not work because it comes with quotation marks, like this:

"/https?://(?:www.|player.)?vimeo.com/(?:channels/(?:w+/)?|groups/([^/]*)/videos/|album/(d+)/video/|video/|)(d+)(?:$|/|?)/"

and when I try to test it, this error is shown...

Uncaught SyntaxError: Invalid regular expression: //https?://(?:www.|player.)?vimeo.com/(?:channels/(?:w+/)?|groups/([^/]*)/videos/|album/(d+)/video/|video/|)(d+)(?:$|/|?)//: Nothing to repeat at String.matc

I've tried to put the regex without the quotation marks on the backend, but the result is the same

What can I do??

Store it as a string literal, with appropriate backslash escaping, then use a regexp constructor when you initialize the regex object. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Mar 17, 2020 at 22:53
@WiktorStribiżew i don't know how to do that, can you show me an example please? — Andres Fernandes
– Andres Fernandes, Commented Mar 17, 2020 at 23:56
Or better, store them as Regex literals: regex: /^.*(youtu.be\/|v\/|u\/\w\/|embed\/|.../ (i.e. drop the surround quotes). — mu is too short
– mu is too short, Commented Mar 18, 2020 at 0:07
@muistooshort that doesn't work for me, if I try to access that without the .to_json I get a "missing / (unclosed regex)" error, I think the problem is that I'm using .to_json, but i dont know — Andres Fernandes
– Andres Fernandes, Commented Mar 18, 2020 at 0:19
Sorry, missed the CoffeeScript part. Why not just write them in CoffeeScript to begin with? Ruby and JavaScript regexes are different anyway. — mu is too short
– mu is too short, Commented Mar 18, 2020 at 1:01

mu is too short · Accepted Answer · 2020-03-18 03:00:36Z

2

There are two separate problems here:

Escaping is going to be a nightmare because everyone (Ruby, (Java|Coffee)Script, regexes) wants to use \ as an escape character.
Converting a dynamic string into a (Java|Coffee)Script regex.

Part (2) is pretty easy, get the regex into a JavaScript string and then use the RegExp constructor in your JavaScript:

# In your CoffeeScript...
str = '^.*(youtu.be\/|v\/|u\/\w\/|embed\/|watch\?v=|&v=)([^#&?]*).*'
re  = new RegExp(str)

So now you need to get this string into your CoffeeScript:

'^.*(youtu.be\/|v\/|u\/\w\/|embed\/|watch\?v=|&v=)([^#&?]*).*'

Build the string in Ruby (using single quotes to reduce the escapes and don't include the leading and trailing slashes):

youtube: {
  regex: '^.*(youtu.be/|v/|u/\w/|embed/|watch\?v=|&v=)([^#&?]*).*'
}

and then you can use to_json to get into JavaScript:

<script type="text/javascript">
  let str = <%= ALLOWED_URLS[:youtube][:regex].to_json %>;
  let re  = new RegExp(str);
</script>

That will be equivalent to saying:

let re = /^.*(youtu.be\/|v\/|u\/\w\/|embed\/|watch\?v=|&v=)([^#&?]*).*/;

in JavaScript.

answered Mar 18, 2020 at 3:00

mu is too short

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2 Comments

Andres Fernandes Over a year ago

Holy cow, thanks! you're a genius! Thank you so much!

Andres Fernandes Over a year ago

Again, thank you, I just finished my task, you're my hero!

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