节点和 Heroku，错误：请求的资源上不存在“Access-Control-Allow-Origin”header

Question

I know this is an usual issue and there are many solutions, however I tried everything and nothing has changed at all. I deployed node and postgresql on Heroku to have a Rest API and fetch it from Angular with HttpClient. I have already deployed it and everything works fine with Postman, however in browser, it shows me this error:

Access to XMLHttpRequest at 'https://myapi.herokuapp.com/products/' from origin 'http://localhost:4200' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

This is my node app:

const express = require('express');
const cors = require('cors');
const app = express();

//MiddleWares
app.use(express.json());
app.use(express.urlencoded({extended:false}));

//Router:
app.use(require('./routes/index'));

const PORT = process.env.PORT || 4000;

const corsOptions = {origin: process.env.URL || '*', credentials: true};

app.use(cors(corsOptions));

app.use((req, res, next) => {
    res.header("Access-Control-Allow-Origin", "*")
    res.header(
      "Access-Control-Allow-Headers",
      "Origin, X-Requested, Content-Type, Accept Authorization"
    )
    if (req.method === "OPTIONS") {
      res.header(
        "Access-Control-Allow-Methods",
        "POST, PUT, PATCH, GET, DELETE"
      )
      return res.status(200).json({})
    }
    next()
  });

app.listen(PORT, err => {
    if(err) throw err;
    console.log('Server on port 4000');
});

This is my package.json:

{
  "name": "backend",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "node src/index.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "cors": "^2.8.5",
    "express": "^4.18.1",
    "pg": "^8.7.3"
  },
  "devDependencies": {
    "nodemon": "^2.0.16"
  }
}

And Angular:

  constructor(
    private http: HttpClient
  ) { }

  getAllProducts() {
    return this.http.get<Product[]>(`${environment.url_api}/products/`);
  }

A browser extension won't help since I will need to deploy the Angular project on a hosting

Answer 1

Thanks for the comments, I already resolved it by removing the cors package and only having a bunch of code for the cors configuration. My node app ended on this:

const express = require('express');
const app = express();


//Cors Configuration - Start
app.use((req, res, next) => {
  res.header("Access-Control-Allow-Origin", "*")
  res.header(
    "Access-Control-Allow-Headers",
    "Origin, X-Requested, Content-Type, Accept Authorization"
  )
  if (req.method === "OPTIONS") {
    res.header(
      "Access-Control-Allow-Methods",
      "POST, PUT, PATCH, GET, DELETE"
    )
    return res.status(200).json({})
  }
  next()
})
//Cors Configuration - End


//Router:
app.use(require('./routes/index'));

const PORT = process.env.PORT || 4000;

app.listen(PORT, err => {
    if(err) throw err;
    console.log('Server on port 4000');
});

As you can see, I didn't use the cors npm package. : I got it from this blog https://medium.com/nerd-for-tech/solving-cors-errors-associated-with-deploying-a-node-js-postgresql-api-to-heroku-1afd94964676/

Answer 2

I just added a Procfile with the next content: 'web: node src/index.js'. I hope it works for you.