Node.js 在类方法中访问时,变量变为未定义
我在构造函数中定义了一个类变量,该构造函数保存对导入的类实例的引用 然而,当我试图访问类方法中的变量时,我总是得到该变量的Node.js 在类方法中访问时,变量变为未定义,node.js,express,undefined,babel-node,Node.js,Express,Undefined,Babel Node,我在构造函数中定义了一个类变量,该构造函数保存对导入的类实例的引用 然而,当我试图访问类方法中的变量时,我总是得到该变量的undefined 导出类 import models from '../../database/models' const {User} = models; class UserRepository { constructor(){ this.model = User; } async create({firstname, lastname, ema
undefined
导出类
import models from '../../database/models'
const {User} = models;
class UserRepository {
constructor(){
this.model = User;
}
async create({firstname, lastname, email, isadmin, password}){
return await this.model.create({firstname, lastname, email, isadmin, password})
}
}
export default new UserRepository();
import repository from './repository';
import { sendSuccessMessage } from '../../utils'
class UserController {
constructor() {
this.model = repository;
}
async createUser({ body }, res, next) {
try {
const result = await this.model.create(body);
sendSuccessMessage(res, 200, result);
} catch( e ){
next(e)
}
}
}
export default new UserController();
使用导出的类初始化
import models from '../../database/models'
const {User} = models;
class UserRepository {
constructor(){
this.model = User;
}
async create({firstname, lastname, email, isadmin, password}){
return await this.model.create({firstname, lastname, email, isadmin, password})
}
}
export default new UserRepository();
import repository from './repository';
import { sendSuccessMessage } from '../../utils'
class UserController {
constructor() {
this.model = repository;
}
async createUser({ body }, res, next) {
try {
const result = await this.model.create(body);
sendSuccessMessage(res, 200, result);
} catch( e ){
next(e)
}
}
}
export default new UserController();
但是,使用createUser
中的变量repository
目录,如下所述:
const result=wait repository.create(body)代码>
一切正常
当前呼叫链
// routes.js file
import controller from './controller'
export default [
{
path: '/signup',
method: 'post',
handlers: [controller.createUser] // createUser from class UserController
}
]
// utitlity.js file
export const routesLoader = (routes, router) => {
for (const route of routes) {
const { path, handlers, method } = route;
(router)[method](path, handlers);
}
};
// app.js file
import express from 'express';
import routes from './routes.js';
import { routesLoader } from './utils';
const router = express.Router();
routesLoader(routes, router);
// server.js file
import http from 'http';
import app from './app';
const { PORT = 3000 } = process.env;
const server = http.createServer(app);
server.listen(PORT, () => {
console.log(`server listening on localhost: ${PORT}`);
});
错误
TypeError: Cannot read property 'create' of undefined
at _callee$ (C:\Users\MYPC\Downloads\moch-shop-api-master\components\user/controller.js:16:39)
at tryCatch (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\regenerator-runtime\runtime.js:45:40)
at Generator.invoke [as _invoke] (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\regenerator-runtime\runtime.js:271:22)
at Generator.prototype.<computed> [as next] (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\regenerator-runtime\runtime.js:97:21)
at asyncGeneratorStep (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\@babel\runtime\helpers\asyncToGenerator.js:3:24)
at _next (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\@babel\runtime\helpers\asyncToGenerator.js:25:9)
at C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\@babel\runtime\helpers\asyncToGenerator.js:32:7
at new Promise (<anonymous>)
at C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\@babel\runtime\helpers\asyncToGenerator.js:21:12
at createUser (C:\Users\MYPC\Downloads\moch-shop-api-master\components\user\controller.js:70:28)
at Layer.handle [as handle_request] (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\express\lib\router\layer.js:95:5)
at next (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\express\lib\router\route.js:137:13)
at Route.dispatch (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\express\lib\router\route.js:112:3)
at Layer.handle [as handle_request] (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\express\lib\router\layer.js:95:5)
at C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\express\lib\router\index.js:281:22
at Function.process_params (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\express\lib\router\index.js:335:12)
at next (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\express\lib\router\index.js:275:10)
at cors (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\cors\lib\index.js:188:7)
at C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\cors\lib\index.js:224:17
at originCallback (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\cors\lib\index.js:214:15)
at C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\cors\lib\index.js:219:13
at optionsCallback (C:\Users\MYPC\Downloads\moch-shop-api-master\node_modules\cors\lib\index.js:199:9)
您的方法create是一个实例方法。它需要是静态的,才能正常工作。首先,您需要在使用它之前正确导入UserRepository
import UserRepository from 'path to UserRepository class';
然后
在函数中使用self
,如下所示:
async createUser({ body }, res, next) {
const self = this;
try {
const result = await self.model.create(body);
sendSuccessMessage(res, 200, result);
} catch( e ){
next(e)
}
}
我认为在createUser()函数中使用self
比使用this
更好。如何调用UserController.createUser
?听起来好像它的这个设置不正确。假设我们初始化了类,如下所示:
const userController = new UserController();
然后,如果您只传递对该方法的精确引用,则缺少此的一个来源可能是
setImmediate(userController.createUser);
而不是保留此
的方式:
setImmediate(() => {
userController.createUser()
});
换言之,您希望使用点表示法为该方法创建发票,并涉及类实例。构造函数是如何在此行中获取UserRepository的。model=UserRepository;Isthis.model=UserRepository
实际上是将类而不是实例分配给this.model
?@VLAZ我认为它是在分配类的实例,因为导出的是实例,而不仅仅是类名。在这种情况下,它是如何导入的?@VLAZ,我刚刚注意到我输入了一个错误。我刚刚更新了这个问题。但是为什么上下文丢失了?@VLAZ,看到这个答案,我的脑海中出现了同样的问题,是不是babel节点
传输的代码是原因?@Deep Kakkar,我仍然有同样的问题,模型
仍然是未定义的
@wokorodueysamuel?奇怪的是,它会这样做,但这并不是不可能的-以前在传输方面有过错误。调用堆栈有点奇怪,因为它显然创建了一个异步生成器。也许这是对的,但还是有点奇怪。我会更新这个问题,包括它是如何发生的called@wokorodouyesamuel谢谢,这确实是个问题:用保留这个的东西替换这个处理程序:[controller.createUser]
,比如,我不知道是否可能,但是:处理程序:[()=>{controller.createUser();}]
感谢您指出,我将更仔细地研究这一点。