How to prevent Next.js from instantiating a singleton class/object multiple times?

Question

I have an analytics utility like this:

class Analytics {
    data: Record<string, IData>;

    constructor() {
        this.data = {};
    }
    setPaths(identifier: string) {
        if (!this.data[identifier])
            this.data[identifier] = {
                generic: getGenericInit(),
                session: getSessionInit(),
                paths: {
                    geoCollectionPath: '',
                    sessionCollectionPath: '',
                    eventsCollectionPath: ''
                }
            };
        this.data[identifier].paths = {
            geoCollectionPath: getGeoPath(identifier),
            sessionCollectionPath: getSessionPath(identifier),
            eventsCollectionPath: getEventPath(identifier)
        };
    }
    getAll() {
        return this.data;
    }
}

const analytics = new Analytics();
export default analytics;

And I import it into 2 api folders: e1.ts and e2.ts.

e1.ts:

import { NextApiHandler } from 'next';
import analytics from '@/firebase/v2/analytics';

const handler: NextApiHandler = (req, res) => {
    analytics.setPaths('abc');
    return res.status(201).end();
};
export default handler;

and e2.ts:

import { NextApiHandler } from 'next';
import analytics from '@/firebase/v2/analytics';

const handler: NextApiHandler = (req, res) => {
    return res.status(200).json(analytics.getAll());
};
export default handler;

Now even when I add the data by hitting /api/e1 since the import instantiates a fresh class in e2, I fail to retrieve the data from /api/e2. How can I achieve my use case for this?

I also tried using static instance but that doesn't work as well. Can someone help me in finding a solution to this?

Youssouf Oumar · Accepted Answer · 2024-02-10 16:05:21Z

16

In development, Next clears Node.js cache on run, so every time there is a "compiling..." in the terminal (which happens per page render), it starts as a new app, losing any previous variable.

This is why, in this article, down to the section where they instantiate a PrismaClient, to have it created only once, they use the global object, in your case, like so:

let analytics;

if (process.env.NODE_ENV === "production") {
  analytics = new Analytics();
} else {
  if (!global.analytics) {
    global.analytics = new Analytics();
  }
  analytics = global.analytics;
}

export default analytics;

edited Feb 10, 2024 at 16:05

answered Jan 29, 2023 at 9:48

Youssouf Oumar

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2 Comments

Sebastian Feb 6 at 11:32

I'd like to add a caveat to this solution. If you're developing with hot module replacement (e.g. using next dev), this will prohibit new code from being loaded. So whenever you make changes to the Analytics class, the first version of the class instance may be stored globally, and any later versions will never be instantiated, so new code won't run unless you restart the dev server. If you're aware of this, then this solution works well.

jmsandiegoo Sep 7 at 3:48

Does this clearing of cache concept applies to Next.js Route Handlers?

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