'this'在express.js路由器中未定義路由器

Question

感謝您花時間閱讀本文。我剛開始使用express.js和打字稿，遇到了令我困惑的問題。我試圖弄清楚爲什麼'This'在CompanyRouter函數中是未定義的。

路由器初始化這樣的：

this.express.use('/api/v1/company', new CompanyRouter(new CompanyService()).router); 

它是一個背景問題，還是express.js把路由器作爲靜態函數？

import {Router, Request, Response, NextFunction} from 'express'; 
import {Company} from '../models/Company'; 
import {ICompanyService} from '../interfaces/ICompanyService'; 

export class CompanyRouter { 
    router: Router 
    service: ICompanyService 

    constructor(service : ICompanyService) { 
     this.router = Router(); 
     this.service = service; 
     this.init(); 
    } 

    init() { 
     this.router.get('/', this.getAllCompanies); 
     this.router.post('/', this.postCompany); 
    } 

    public async getAllCompanies(req: Request, res: Response, next: NextFunction) { 
     const companies = this.service.findAll() 
     res.send(companies); 
    } 

    public async postCompany(req: Request, res: Response, next: NextFunction) { 
     const company = this.service.add(req.body); 
     res.send(company); 
    } 
} 

Answer 1

此問題與您的方法在您的init()函數中如何被調用有關。傳遞函數的引用而不是直接調用它會使this未定義，因爲它失去了引用。

所以，我認爲下面的代碼應該工作：

import {Router, Request, Response, NextFunction} from 'express'; 
import {Company} from '../models/Company'; 
import {ICompanyService} from '../interfaces/ICompanyService'; 

export class CompanyRouter { 
    router: Router 
    service: ICompanyService 

    constructor(service : ICompanyService) { 
     this.router = Router(); 
     this.service = service; 
     this.init(); 
    } 

    init() { 
     this.router.get('/', (req, res, next) => this.getAllCompanies(req, res, next)); 
     this.router.post('/', (req, res, next) => this.postCompany(req, res, next)); 
    } 

    public async getAllCompanies(req: Request, res: Response, next: NextFunction) { 
     const companies = this.service.findAll() 
     res.send(companies); 
    } 

    public async postCompany(req: Request, res: Response, next: NextFunction) { 
     const company = this.service.add(req.body); 
     res.send(company); 
    } 
}