React + fetch request - angularjs

Question

I am reading this article fetch API and trying to understand how to work with fetch in React. Firstly, could you explain what is request headers ?
Than,
in angular we do something like:
$http.get('/someword').success(function(response) {
console.log('i got the data i requested');
var variable = response;
}
and than on server side in express I can write:
var app = express();
app.get('/thissomeword', function(req, res) {
console.log('I got a GET request')
res.json(someVariableWithData)
})
How to do the same with fetch ? And the main question where and when I need to do it ? I understand that i need after i get data to do this.setState({}) for using my data later, but HOW is for me huge conundrum.

Answer 1

Here you have great facebook documentation:
https://facebook.github.io/react-native/docs/network.html
with example that shows what you want
headers in request
Sometimes you need header in request to provide access token or content-type (especially in POST request)
fetch('https://mywebsite.com/endpoint/', {
method: 'POST',
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json',
},
body: JSON.stringify({
firstParam: 'yourValue',
secondParam: 'yourOtherValue',
})
})
Promises instead of callbacks
In your example you pass callbacks (req and res) to your request, in fetch you have Promises so you get response as a paramether of then or error message in catch.
fetch('https://facebook.github.io/react-native/movies.json')
.then((response) => response.json())
.then((responseJson) => {
return responseJson.movies;
})
.catch((error) => {
console.error(error);
});

Answer 2

Request Headers
As basic, Request Headers are set by the browsers and the application developers, this is use to tell the web server what the client is sending and what can it accept back in return.
Reference
Fetch
Fetch is used to make async network calls. It has a simpler API support based on promises. I'll make your code cleaner with less number of lines.
Reference