An ECMAScript proposal. Currently at Stage 0.

This proposal was brought before the committee in the March 2016 meeting, and thoroughly rejected. Details

Here is the current situation:

var s = new Set(['yo', 'ya', true, 8]);

console.log(JSON.stringify(s)); // '{}'

This result is unhelpful. Same goes for Map.

This proposal is about providing a sensible default to the common operation of JSON serialization via default toJSON implementations on Set.prototype and Map.prototype. Of course, userland code can always shadow this value on specific instances.

The essence of the proposal is captured in this snippet (spec in markdown or HTML):

Map.prototype.toJSON = function toJSON() {
  return [...Map.prototype.entries.call(this)];
}

The essence of the proposal is captured in this snippet (spec in markdown or HTML):

Set.prototype.toJSON = function toJSON() {
  return [...Set.prototype.values.call(this)];
}

There might be a web compat concern if code using native Map and Set or polyfill relies on the current JSON.stringify behavior.

This work is dedicated to the public domain. It is CC0 licenced.