express-lazy-router/module/express-lazy-router.js

Lazy loading for express router

import express from "express";
/**
 * @param options
 * @example
 * ```js
 * const lazyLoad = createLazyLoader();
 * router.use(
 *   '/path_to_router',
 *   lazyLoad(() => import('./path_to_router')),
 * );
 * ```
 */
export function createLazyRouter(options) {
    var _a;
    if (options === void 0) { options = {}; }
    var preload = (_a = options.preload) !== null && _a !== void 0 ? _a : false;
    /**
     * lazy load express router
     * @param resolver
     */
    return function lazyRouter(resolver) {
        var lazyRouter = express.Router();
        // Preserve loading order of router for default error handler
        // https://github.com/azu/express-lazy-router/issues/1
        var loadedRouter;
        var resolveResolver = function () {
            return resolver().then(function (router) {
                if (!router) {
                    throw new Error("lazyLoad(resolver) the resolver function should return a promise object, but it returns falsy value: " + router + "\n\nYou need to return a promise object from the callback function.\n\n    lazyLoad(() => import('./path_to_router')),                \n");
                }
                if ("default" in router) {
                    loadedRouter = router.default;
                }
                else {
                    loadedRouter = router;
                }
            });
        };
        lazyRouter.use(function lazyRouterHandler(req, res, next) {
            if (loadedRouter) {
                return loadedRouter(req, res, next);
            }
            else {
                // request handler at first time
                resolveResolver()
                    .then(function () {
                    return loadedRouter(req, res, next);
                })
                    .catch(function (error) {
                    next(error);
                });
            }
        });
        if (preload) {
            resolveResolver().catch(function (error) {
                console.error("[lazy-router] Fail to preload", error);
            });
        }
        return lazyRouter;
    };
}
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