Using Fetch​

React Native provides theFetch API for your networking needs. Fetch will seem familiar if you have usedXMLHttpRequest or other networking APIs before. You may refer to MDN's guide onUsing Fetch for additional information.

Making requests​

In order to fetch content from an arbitrary URL, you can pass the URL to fetch:

fetch('https://mywebsite.com/mydata.json');

Fetch also takes an optional second argument that allows you to customize the HTTP request. You may want to specify additional headers, or make a POST request:

fetch('https://mywebsite.com/endpoint/',{
  method:'POST',
  headers:{
Accept:'application/json',
'Content-Type':'application/json',
},
  body:JSON.stringify({
    firstParam:'yourValue',
    secondParam:'yourOtherValue',
}),
});

Take a look at theFetch Request docs for a full list of properties.

Handling the response​

The above examples show how you can make a request. In many cases, you will want to do something with the response.

Networking is an inherently asynchronous operation. Fetch method will return aPromise that makes it straightforward to write code that works in an asynchronous manner:

constgetMoviesFromApi=()=>{
returnfetch('https://reactnative.dev/movies.json')
.then(response=> response.json())
.then(json=>{
return json.movies;
})
.catch(error=>{
console.error(error);
});
};

You can also use theasync /await syntax in a React Native app:

constgetMoviesFromApiAsync=async()=>{
try{
const response=awaitfetch(
'https://reactnative.dev/movies.json',
);
const json=await response.json();
return json.movies;
}catch(error){
console.error(error);
}
};

Don't forget to catch any errors that may be thrown byfetch, otherwise they will be dropped silently.

Using Other Networking Libraries​

TheXMLHttpRequest API is built into React Native. This means that you can use third party libraries such asfrisbee oraxios that depend on it, or you can use the XMLHttpRequest API directly if you prefer.

const request=newXMLHttpRequest();
request.onreadystatechange= e=>{
if(request.readyState!==4){
return;
}

if(request.status===200){
console.log('success', request.responseText);
}else{
console.warn('error');
}
};

request.open('GET','https://mywebsite.com/endpoint/');
request.send();

WebSocket Support​

React Native also supportsWebSockets, a protocol which provides full-duplex communication channels over a single TCP connection.

const ws=newWebSocket('ws://host.com/path');

ws.onopen=()=>{
// connection opened
  ws.send('something');// send a message
};

ws.onmessage= e=>{
// a message was received
console.log(e.data);
};

ws.onerror= e=>{
// an error occurred
console.log(e.message);
};

ws.onclose= e=>{
// connection closed
console.log(e.code, e.reason);
};

Known Issues withfetch and cookie based authentication​

The following options are currently not working withfetch

• redirect:manual
• credentials:omit

• Having same name headers on Android will result in only the latest one being present. A temporary solution can be found here:https://github.com/facebook/react-native/issues/18837#issuecomment-398779994.
• Cookie based authentication is currently unstable. You can view some of the issues raised here:https://github.com/facebook/react-native/issues/23185
• As a minimum on iOS, when redirected through a302, if aSet-Cookie header is present, the cookie is not set properly. Since the redirect cannot be handled manually this might cause a scenario where infinite requests occur if the redirect is the result of an expired session.

Configuring NSURLSession on iOS​

For some applications it may be appropriate to provide a customNSURLSessionConfiguration for the underlyingNSURLSession that is used for network requests in a React Native application running on iOS. For instance, one may need to set a custom user agent string for all network requests coming from the app or supplyNSURLSession with an ephemeralNSURLSessionConfiguration. The functionRCTSetCustomNSURLSessionConfigurationProvider allows for such customization. Remember to add the following import to the file in whichRCTSetCustomNSURLSessionConfigurationProvider will be called:

#import<React/RCTHTTPRequestHandler.h>

RCTSetCustomNSURLSessionConfigurationProvider should be called early in the application life cycle such that it is readily available when needed by React, for instance:

-(void)application:(__unused UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions{

// set RCTSetCustomNSURLSessionConfigurationProvider
RCTSetCustomNSURLSessionConfigurationProvider(^NSURLSessionConfiguration*{
     NSURLSessionConfiguration*configuration=[NSURLSessionConfiguration defaultSessionConfiguration];
// configure the session
return configuration;
});

// set up React
  _bridge=[[RCTBridge alloc] initWithDelegate:self launchOptions:launchOptions];
}