Serialization of RegExp
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;// samplevar foo = { rgx: /qux$/ig, date: new Date }JSON.stringify(foo);//> {"rgx":"/qux$/gi","date":"2014-03-21T23:11:33.749Z"}"
Both JSON.stringify and JSON.parse can be customized to do custom serialization and deserialization by using the replacer and reviver arguments.
var o = { foo: "bar", re: /foo/gi};function replacer(key, value) { if (value instanceof RegExp) return ("__REGEXP " + value.toString()); else return value;}function reviver(key, value) { if (value.toString().indexOf("__REGEXP ") == 0) { var m = value.split("__REGEXP ")[1].match(/\/(.*)\/(.*)?/); return new RegExp(m[1], m[2] || ""); } else return value;}console.log(JSON.parse(JSON.stringify(o, replacer, 2), reviver));You just have to come up with your own serialization format.
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.