How to make a fetch request to localhost in React Native/Expo? - react-native

Question

I'm creating a React Native/Expo app that uses Deno on the backend. I've created an API in the backend that I can run locally on localhost:4000. When I try to use fetch to call the API in the Expo app, however, I keep getting an error
[Unhandled promise rejection: TypeError: Network request failed] at node_modules/whatwg-fetch/dist/fetch.umd.js:535:17 in setTimeout$argument_0
Here is how I set up the backend
import { Application } from "https://deno.land/x/oak/mod.ts";
import { oakCors } from "https://deno.land/x/cors/mod.ts";
import { APP_HOST, APP_PORT } from "./config.ts";
import router from "./routes.ts";
import _404 from "./controllers/404.ts";
import errorHandler from "./controllers/errorHandler.ts";
const app = new Application();
app.use(oakCors());
app.use(errorHandler);
app.use(router.routes());
app.use(router.allowedMethods());
app.use(_404);
console.log(`Listening on port:${APP_PORT}...`);
And how I use fetch to call the API
const App = () => {
const getData = async () => {
const response = await fetch("http://localhost:4000/something");
const data = await response.json();
console.log(data);
};
useEffect(() => {
getData();
}, []);
return (
...
);
};
Note
Some answers on StackOverflow suggest fetching http://[IP_ADDRESS]:4000/something instead of localhost. I've tried that with no luck.
I've verified that the API is working. I can call it successfully in VSCode's Thunder Client and I can also see the data by going to http://localhost:4000 in the browser.

Answer 1

I found a solution to this issue. I'm running my Expo app on a physical device while my server is running on my computer, on localhost. It makes sense that I'm unable to make requests to localhost on my device, because localhost is not running there.
I fixed this issue by using ngrok, a tool that forwards localhost to a cloud URL, and fetching that URL in the app.

Answer 2

Use the local IP assign to your device, like: http://192.168.20.109:port/api/x
find the local IP using the command "ipconfig" in windows or ifconfig in linux