I've seen people use code that looks like
const STUFF_MAP = Object.create(null);
STUFF_MAP would like suggested only be used like a map, so I understand why using Object.create(null) is better than {} (removing the properties that could cause conflicts etc.), but is there any advantage to not just use
const STUFF_MAP = new Map();
When would I use each one? Does it have to do with being compiled to pre es6?
Does it have to do with being compiled to pre es6?
Yes, Object.create(null) is ES5 and won't need a polyfill for Map, if you need to support old browsers.
Apart from that, you should prefer the more modern Map which is also clearly indicates the purpose of a variable. You will need to access the collection using has/get/set methods, not in operator/bracket syntax/assignment. This can sometimes lead to code that isn't as concise, e.g. for incrementing a value you cannot use a compound assignment operator.
As for performance, there should not be much of a difference; if you care, do a benchmark for your particular situation.