Networking - Amazon Vega Docs

Many mobile apps need to load resources from a remote URL. You may want to make a POST request to a REST API, or you may need to fetch a chunk of static content from another server.

Using Fetch

React Native provides the Fetch API for your networking needs. Fetch will seem familiar if you have used XMLHttpRequest or other networking APIs before. You may refer to MDN’s guide on Using 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',
  }),
});

const formData = new FormData();
formData.append('firstParam', 'yourValue');
formData.append('secondParam', 'yourOtherValue');

fetch('https://mywebsite.com/endpoint/', {
  method: 'POST',
  headers: {
    Accept: 'application/json',
    "Content-Type": "multipart/form-data",
  },
  body: formData,
});

Take a look at the Fetch 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 a Promise that makes it straightforward to write code that works in an asynchronous manner:

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

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

const getMoviesFromApiAsync = async () => {
  try {
    const response = await fetch(
      '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 by fetch, otherwise they will be dropped silently.

import React, {useEffect, useState} from 'react';
import {ActivityIndicator, FlatList, Text, View} from 'react-native';

const App = () => {
  const [isLoading, setLoading] = useState(true);
  const [data, setData] = useState([]);

  const getMovies = async () => {
    try {
      const response = await fetch('https://reactnative.dev/movies.json');
      const json = await response.json();
      setData(json.movies);
    } catch (error) {
      console.error(error);
    } finally {
      setLoading(false);
    }
  };

  useEffect(() => {
    getMovies();
  }, []);

  return (
    <View style={{flex: 1, padding: 24}}>
      {isLoading ? (
        <ActivityIndicator />
      ) : (
        <FlatList
          data={data}
          keyExtractor={({id}) => id}
          renderItem={({item}) => (
            <Text>
              {item.title}, {item.releaseYear}
            </Text>
          )}
        />
      )}
    </View>
  );
};

export default App;

import React, {useEffect, useState} from 'react';
import {ActivityIndicator, FlatList, Text, View} from 'react-native';

type Movie = {
  id: string;
  title: string;
  releaseYear: string;
};

const App = () => {
  const [isLoading, setLoading] = useState(true);
  const [data, setData] = useState<Movie[]>([]);

  const getMovies = async () => {
    try {
      const response = await fetch('https://reactnative.dev/movies.json');
      const json = await response.json();
      setData(json.movies);
    } catch (error) {
      console.error(error);
    } finally {
      setLoading(false);
    }
  };

  useEffect(() => {
    getMovies();
  }, []);

  return (
    <View style={{flex: 1, padding: 24}}>
      {isLoading ? (
        <ActivityIndicator />
      ) : (
        <FlatList
          data={data}
          keyExtractor={({id}) => id}
          renderItem={({item}) => (
            <Text>
              {item.title}, {item.releaseYear}
            </Text>
          )}
        />
      )}
    </View>
  );
};

export default App;

Using other networking libraries

The XMLHttpRequest API is built into React Native. This means that you can use third party libraries such as frisbee or axios that depend on it, or you can use the XMLHttpRequest API directly if you prefer.

const request = new XMLHttpRequest();
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();

The security model for XMLHttpRequest is different than on web as there is no concept of CORS in native apps.

WebSocket support

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

const ws = new WebSocket('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);
};

Encoding support

Fetch internally supports URL encoding as per RFC2396. For additional information, see MDN’s guide on encodeURI. The following options are currently not working with fetch:

redirect:manual
credentials:omit
Cookie based authentication is currently unstable. For additional information, see the issues raised on GitHub at https://github.com/facebook/react-native/issues/23185.

​Using Fetch

​Making requests

​Handling the response

​Using other networking libraries

​WebSocket support

​Encoding support

​Known issues with fetch and cookie based authentication