How would one JSON.stringify() a Set?
Things that did not work in Chromium 43:
var s = new Set(['foo', 'bar']);
JSON.stringify(s); // -> "{}"
JSON.stringify(s.values()); // -> "{}"
JSON.stringify(s.keys()); // -> "{}"
I would expect to get something similar to that of a serialized array.
JSON.stringify(["foo", "bar"]); // -> "["foo","bar"]"
JSON.stringify doesn't directly work with sets because the data stored in the set is not stored as properties.
But you can convert the set to an array. Then you will be able to stringify it properly.
Any of the following will do the trick:
JSON.stringify([...s]);
JSON.stringify([...s.keys()]);
JSON.stringify([...s.values()]);
JSON.stringify(Array.from(s));
JSON.stringify(Array.from(s.keys()));
JSON.stringify(Array.from(s.values()));
You can pass a "replacer" function to JSON.stringify:
const fooBar = {
foo: new Set([1, 2, 3]),
bar: new Set([4, 5, 6])
};
JSON.stringify(
fooBar,
(_key, value) => (value instanceof Set ? [...value] : value)
);
Result:
"{"foo":[1,2,3],"bar":[4,5,6]}"
toJSON is a legacy artifact, and a better approach is to use a custom replacer, see https://github.com/DavidBruant/Map-Set.prototype.toJSON/issues/16
While all of the above work I suggest that you subclass set and add a toJSON method to make sure that it stringify's correctly. Especially if you are going to be stringifying often. I use sets in my Redux stores and needed to make sure this was never a problem.
This is a basic implementation. Naming is just to illustrate the point pick your own style.
class JSONSet extends Set {
toJSON () {
return [...this]
}
}
const set = new JSONSet([1, 2, 3])
console.log(JSON.stringify(set))