In order to access the data from a ReadableStream you need to call one of the conversion methods (docs available here).
As an example:
fetch('https://jsonplaceholder.typicode.com/posts/1')
.then(function(response) {
// The response is a Response instance.
// You parse the data into a useable format using `.json()`
return response.json();
}).then(function(data) {
// `data` is the parsed version of the JSON returned from the above endpoint.
console.log(data); // { "userId": 1, "id": 1, "title": "...", "body": "..." }
});
EDIT: If your data return type is not JSON or you don't want JSON then use text()
As an example:
fetch('https://jsonplaceholder.typicode.com/posts/1')
.then(function(response) {
return response.text();
}).then(function(data) {
console.log(data); // this will be a string
});
Hope this helps clear things up.