Why my cors handling in express doesn't work?

Question

I want to get my data using using express. Here's the code:

const express = require('express');
const app = express();
const cors = require('cors');
require('dotenv/config');

// Middlewares
app.use(cors());
app.use(express.json());

// Routes
const postRouter = require('./routes/posts');
app.use('/posts', postRouter);

// Mongoose connect
const mongoose = require('mongoose');
mongoose.connect(
    process.env.DB_CONNECTION,
    { useNewUrlParser: true },
    () => console.log("You are connected to MongoDB")
);

// Port listen
app.listen(2998);

These node+express code works perfect using Postman.

But it always show CORS error when im fetching using javascript. Here's the JS code:

let url = "https://localhost:2998/posts/"
    fetch(url)
    .then(result => {
        console.log(result);    
    })
    .then(data => {
        console.log("data: " + data)
    });

And the console says:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://localhost:2998/posts/. (Reason: CORS request did not succeed).

. . . . .

SOLVED ! It just can't run the https protocol, so i need to change it to http://localhost/2998. Still, I don't know why it happen to be like that

Answer 1

I believe you did not set the CORS options. Please try the following:

const express = require('express');
const app = express();
const cors = require('cors');
require('dotenv/config');

// CORS Options: But customise according to your needs
const options = {
    allowedHeaders: ["Origin", "Content-Type", "Accept", "Authorization"],
    methods: "GET,HEAD,OPTIONS,PUT,PATCH,POST,DELETE",
    origin: "*",
    preflightContinue: false
};

// Middlewares
app.use(cors(options));
app.use(express.json());

// Routes
const postRouter = require('./routes/posts');
app.use('/posts', postRouter);

// Mongoose connect
const mongoose = require('mongoose');
mongoose.connect(
    process.env.DB_CONNECTION,
    { useNewUrlParser: true },
    () => console.log("You are connected to MongoDB")
);

// Port listen
app.listen(2998);