So, I was interested to find that JSON.stringify reduces a RegExp to an empty object-literal (fiddle):
JSON.stringify(/^[0-9]+$/) // "{}"
Is this behavior expected? I realize that a RegExp is an object with no properties to serialize. That said, dates are objects too; yet JSON.stringify() manages to produce a meaningful string:
JSON.stringify(new Date) // "2014-07-03T13:42:47.905Z"
I would have hoped that JSON would give RegExp the same consideration by using RegExp.prototype.toString().
Answer
If somebody would be interested, there is a nice workaround. I don't think, that current behaviour is correct. For example, Date instance is not serialized to empty object like RegExp, though it is an object and also has no JSON representation.
RegExp.prototype.toJSON = RegExp.prototype.toString;
// sample
var foo = { rgx: /qux$/ig, date: new Date }
JSON.stringify(foo);
//> {"rgx":"/qux$/gi","date":"2014-03-21T23:11:33.749Z"}"