收到javascript / typescript错误“无法读取未定义的属性'Items'”

Question

I am getting an error "Cannot read property 'Items' of undefined" in javascript. this keyword is always undefined in the Base class.

how to resolve this issue? Is there any issue with static method to use in express router?

Typescript compile option is pointing to ES6 .

import * as express from 'express';
import {Router, Request, Response, NextFunction, Wrap } from '../../../Core';
import {FacadeRequest} from '../../../Common';

class Base {
    public Items: any = { Name: 'Natarajan Ganapathi' };
    public Get(): any {
        return this.Items;
    }
}

class User extends Base {
    public GetUsers(): any {
        return super.Get();
    }
}

export type BoRegistry = { [key: string]: () => any };

export class Facade {
    public static BoRegistry: BoRegistry = {};
    public static async GetData(req: Request, res: Response, next: NextFunction): Promise<any> {
        let promises: Array<any> = [];
        let reqs = req.body as Array<FacadeRequest>;
        reqs.forEach(fReq => {
            let route = Facade.ParseRoute(fReq.Route);
            let func = Facade.BoRegistry[route.BoName];
            if (!func) {
                throw new Error(route.BoName + ' not register in BoRegistry');
            }
            let bo = func();
            promises.push(Facade.Invoke(bo, route, fReq));
        });
        return await Promise.all(promises);
    }

    private static async Invoke(bo: any, route: { BoName: string, MethodName: string }, fReq: FacadeRequest): Promise<any> {
        let api = bo[route.MethodName];
        if (!api) {
            throw new Error(route.MethodName + ' is not available in ' + route.BoName);
        }
        let res = await api(fReq.Request);
        return { [fReq.Key]: res };
    }

    private static ParseRoute(route: string): { BoName: string, MethodName: string } {
        let r = route.split('/');
        if (r.length < 2 || r.length > 2) {
            throw new Error('Request contains improper route');
        }
        return { BoName: r[0], MethodName: r[1] };
    }
}

Facade.BoRegistry['User'] = () => new User();

let router: Router = express.Router();
router.post('/' + Facade.GetData.name, Wrap(Facade.GetData));
export default router;

{
"Message": "Cannot read property 'Items' of undefined",
"Stack": "TypeError: Cannot read property 'Items' of undefined\n    
at Get (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:17:20)\n    
at GetUsers (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:22:22)\n    
at Function.<anonymous> (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:48:29)\n    
at next (native)\n    at __awaiter (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:7:65)\n    
at __awaiter (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:3:12)\n    
at Function.Invoke (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:43:16)\n    
at Base.static.GetData.reqs.forEach.fReq (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:37:38)\n    
at Array.forEach (native)\n    
at /Users/dist/dev/Server/Modules/Base/Router/Facade.js:30:18\n    
at next (native)\n    at __awaiter (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:7:65)\n    
at __awaiter (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:3:12)\n    
at GetData (/Users/dist/dev/Server/Modules/Base/Router/Facade.js:27:16)\n    
at exports.Wrap (/Users/dist/dev/Server/Core/Core.js:70:16)\n    
at Layer.handle [as handle_request] (/Users/node_modules/router/lib/layer.js:93:5)"
 }

Answer 1

"Cannot read property 'Items' of undefined",

Common JavaScript error. You need to be cautions of your usage of this or just use an arrow function.

More

https://basarat.gitbooks.io/typescript/content/docs/arrow-functions.html