Using JS weakmaps as cache (Node)

user.js

const cache = new WeakMap();

// This pattern allows us to pass down a single argument (req) down our function chain.
// Then each function/class can get their dependencies in this way - and we know it'll only call
// our DB/storage once per request.
export async function getUserFromReq(req) {
    if (cache.has(req)) {
        return cache.get(req);
    }

    return await User.get(req.form.session_id);
}