How to correctly write lambda expression in fetch - reactjs

Question

I have simple fetch in my react.js project:
export function getUserById(id) {
const requestOptions = {
method: 'GET',
headers: { 'Content-Type': 'application/json','Access-Control-Allow-Origin':'http://localhost:9000' },
mode: 'no-cors',
};
var res = fetch("http://localhost:9000/user/"+id);//there should be a lot of strange lambdas..
return res;
}
I use this function in other file:
var user = getUserById(userStr);
//some code
//more code
var email=user.mail;
var id = user.id;
Unfortunately - res is always Promise. I don't feel functional programming and react but I need to do it. I know that there should be some lambda expression, but I have no idea how to write them. As you see I need to take email and id from returning JSON.
Thanks in advance.

Answer 1

You need to await the fetch call.
See this example on MDN.
export async function getUserById(id) {
const requestOptions = {
method: 'GET',
headers: { 'Content-Type': 'application/json','Access-Control-Allow-Origin':'http://localhost:9000' },
mode: 'no-cors',
};
var res = fetch("http://localhost:9000/user/"+id);//there should be a lot of strange lambdas..
return res;
}
var user = await getUserById(userStr);
//some code
//more code
var email=user.mail;
var id = user.id;
Edit: You don’t need to await the fetch call, you only need to await getUserById(userStr).

Answer 2

Answer is not that easy. Proper way (await returns promise!) is little bit more problematic. There is my solve ;) :
return fetch("http://your.fancy.link").then((response) => response.json())
and
function App() {
const [state, setState] = useContext(MyContext);
const [loading,setLoading] = useState(true);
const readUrlParamsFromAuthentication = () => {
var url_string = window.location.href; //window.location.href
var url = new URL(url_string);
var userStr = url.searchParams.get("user-id");
var userId = null;
var userEmail = null;
if (userStr) {
getUserById(userStr).then(user=>
{
localStorage.setItem('email', user.email);
setState({ email: user.email, isLogged: true });
console.log("TUTAAAAJ");
console.log(user.email,user.id,state.isLoggedIn);
setLoading(false);
}
);
console.log("UserStr");
}
}
useEffect(() => {
readUrlParamsFromAuthentication();
}, [])
there should be your return html ;)