remix-utils/build/server/middleware/singleton.js

This package contains simple utility functions to use with [React Router](https://reactrouter.com/).

import { unstable_createContext } from "react-router";
/**
 * Creates a singleton middleware that creates an instance of a class and stores
 * it in the context. If the instance already exists in the context, it will
 * return the existing instance.
 *
 * @param options - Options for the singleton middleware.
 * @param options.Class - The class to create an instance of.
 * @param options.arguments - Arguments to pass to the class constructor.
 * @returns A tuple containing the middleware function and a function to get the
 * singleton instance from the context.
 */
export function unstable_createSingletonMiddleware(options) {
    let singletonContext = unstable_createContext(null);
    return [
        async function singletonMiddleware({ context }, next) {
            let instance = context.get(singletonContext);
            if (instance)
                return await next();
            instance = new options.Class(...options.arguments);
            context.set(singletonContext, instance);
            return await next();
        },
        function getSingletonInstance(context) {
            let instance = context.get(singletonContext);
            if (!instance)
                throw new Error("Singleton instance not found");
            return instance;
        },
    ];
}
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