Access to fetch at from origin 'http://localhost:3000' has been blocked by CORS policy

Question

Adding to the database shows the error. what should I do?

Access to fetch at 'http:xxx' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

my function:

addItem = (e) => {
    e.preventDefault();
    const ob = {
        X: 53.0331258,
        Y: 18.7155611,
    }
    fetch("http://xxx", {
            method: "post",
            headers: {
                "Content-Type": "application/json"
            },
            body: JSON.stringify(ob)
        })
        .then(res => res.json())
        .then(res => {
            console.log(res);
        })
}

Solution 1

try using ''no-cors' mode.

fetch('http://localhost:8080/example', {
            mode: 'no-cors',
            method: "post",
            headers: {
                 "Content-Type": "application/json"
            },
            body: JSON.stringify(ob)
 })

Solution 2

Your server should respond with a response that looks like below

Access-Control-Allow-Origin: https://localhost:3000

Untill you are able to configure that as a workaround you can install the below chrome extension to resume your testing

https://chrome.google.com/webstore/detail/who-cors/hnlimanpjeeomjnpdglldcnpkppmndbp?hl=en-GB

But the above is only a workaround to continue development

I would suggest you read this article for understanding CORS https://javascript.info/fetch-crossorigin

Solution 3

I resolved the issue by installing the cors node module and adding this on the requested server

const cors = require("cors");
app.use(cors());

Solution 4

You must install cors.

npm install cors

inside the main scripts index.js or app.js

const cors = require("cors");
app.use(cors());

Solution 5

For browser CORS is enabled by default and you need to tell the Browser it's ok for send a request to server that not served your client-side app ( static files ).

if you use RestFul API with node and express add this middleware to your file

app.use((req, res, next) => {
  res.header("Access-Control-Allow-Origin", "*")
}) 

View more solutions

Comments

[happyZZR1400]

when you trying to make request from different domain (xxx in your case)the browser not allow to send such request. if xxx is your server - you can configure it to send the headers that allows cros domain request

[Jonathan]

It actually tells you what the issue is. See stackoverflow.com/a/10636765/12989672

[Heretic Monkey]

Does this answer your question? How does Access-Control-Allow-Origin header work?

[Saurav Seth]

I thought localhost was now granted an exception from CORS restrictions on modern browsers including Chrome. You are pulling in your HTML directly from a web server and not from a local source file are you?

[William]

app is not defined

[ABDERRAHMANE OUALI]

you should first import express at the top by; const express = require("express"); then const app = express();

[K.K Desgins]

What would be the point of a security system with a button saying "disable me" on the outside? See Trying to use fetch and pass in mode: no-cors — { mode: 'no-cors' } makes things worse.

[White Rabbit]

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