Some async handler.

async.js

// If I don't care about the status code
function fetchJSON(...params) {
  return fetch(...params).then(res => res.json());
}

// If I do care about the status code, but don't care about the type of error.
async function fetchJSON(...params) {
  const res = await fetch(...params);
  if (res.status >= 400) {
    throw new Error(res.statusText);
  }
  return res.json();
}

// If I care about any errors.
async function fetchJSON(...params) {
  const res = await fetch(...params);
  if (res.status >= 400) {
    return {
      error: { status: res.status, statusText: res.statusText };
    }
  }
  return { data: res.json() };
}

// In the last example, I'd use the function like this (assuming I'm in an async function):

const { data, error } = await fetchJSON(...params);
if (error) {
  // Do stuff here.
}

// Do stuff with data here.