When I run the following code:
fake_key = new Set([{v: 1, w: 2}])
fake_memo = {};
fake_memo[fake_key] = 2;
fake_key = new Set([{v: 5, w: 5}])
fake_memo[fake_key] = 5;
And then print or log fake_memo, I expect to see:
{ '[object Set]': 2, '[object Set]': 5 }
Instead I get:
{ '[object Set]': 5 }
As if the first object I inserted into the object map got clobbered by the second.
Why does this occur? How do I recover the behavior I want (both keys being inserted into the map)?
Property keys of plain objects are always strings. Your sets are being converted to strings, which always gives the string "[object Set]".
You can instead use a Map instance instead of a plain object, because Map keys can be any type of value. To do that, make a map:
fake_memo = new Map();
then
fake_memo.set(fake_key, 2);
etc. Use
var value = fake_memo.get(some_key);
to retrieve values.
You can use ordinary [ ] operations on a Map instance, but that will still treat the Map as an ordinary object.
fake_memo = new Map();, unfortunately. More specifically, I now see Map { '[object Set]': 5 }.
As another answer said, keys can only be strings. So this may be what you are looking for:
fake_key = JSON.stringify(Array.from(new Set([{v: 1, w: 2}])));
fake_memo = {};
fake_memo[fake_key] = 2;
fake_key = JSON.stringify(Array.from(new Set([{v: 5, w: 5}])));
fake_memo[fake_key] = 5;
'[object Set]'.