Question

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 1

Yes, because there’s no canonical representation for a RegExp object in JSON. Thus, it’s just an empty object.

edit — well it’s 2018 now; the answers suggesting solutions using .toJSON() etc are probably fine, though I’d add the method to the prototype with

Object.defineProperty(RegExp.prototype, "toJSON", {
  value: RegExp.prototype.toString
});

and so on. That ensures that the function name isn’t enumerable, which makes the monkey-patch somewhat more hygienic.