Passing RegExp objects between content scripts and main add-on script

Question

I am having an issue whereby I create a RegExp object in a content script and pass it as part of an object back to the main script using self.port.emit(). Somewhere along the way it seems to lose its identity as a RegExp and also its toString abilities. The following returns false in the main script, but true in the content script:

Object.prototype.toString.call(regexp) == '[object RegExp]';
regexp instanceof RegExp;

Interestingly for Arrays passed in the same way the following is true:

Object.prototype.toString.call(array) == '[object Array]';

Am I missing something?

At least in Chrome, trying to covert an expression to JSON results in an empty object: {foo: /test/} becomes "{"foo":{}}". JSON does not know regex types. I assume the same is happening in your case. — Felix Kling
– Felix Kling, Commented Aug 20, 2012 at 10:01

Wladimir Palant · Accepted Answer · 2012-08-20 15:08:29Z

1

The Add-on SDK doesn't pass objects around when you send messages, only strings - it essentially calls JSON.stringify() on one side and then JSON.parse() on the other. The result is easy to predict:

console.log(JSON.stringify(new RegExp()));

This gives you "{}". In other words, JSON.stringify() treats "custom" objects as normal objects without any properties, object prototypes and such are ignored. What you get in your main code is a plain object, same as if you call new Object().

If you need to pass a regular expression to your main code - send regexp.source, create an actual regular expression on the other side. Sending actual objects around isn't possible.

answered Aug 20, 2012 at 15:08

Wladimir Palant

57.8k12 gold badges100 silver badges129 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Arth Over a year ago

Thanks, are you sure about "JSON.stringify() treats "custom" objects as normal objects without any properties" though? Any custom defined fields seem to be preserved.

Wladimir Palant Over a year ago

@Arth: Well, custom properties are preserved - but regexp-specific ones (meaning: defined on the prototype) aren't.

Yansky · Accepted Answer · 2012-08-20 11:15:15Z

1

What about if you just sent the regex pattern instead of the whole rexexp object? e.g. encodeURIComponent(regexp.source);

answered Aug 20, 2012 at 11:15

Yansky

4,8108 gold badges31 silver badges24 bronze badges

1 Comment

Arth Over a year ago

I didn't want to target the regexp specifically because the JSON object gets recursively turned into a custom script at the other end and includes strings and Arrays. I think I prefer JSON.stringify() to URI encoding, but this is basically what I have done.

Collectives™ on Stack Overflow

Passing RegExp objects between content scripts and main add-on script

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related