set custom user agent react

1let headers = new Headers({
2    "Accept"       : "application/json",
3    "Content-Type" : "application/json",
4    "User-Agent"   : "MY-UA-STRING"
5});
6
7fetch(url, {
8    method  : 'GET', 
9    headers : headers 
10    // ... etc
11}).then( ...
12