Use fetch if XMLHttpRequest not available

[paularmstrong]

Do you want to request a feature or report a bug?
Feature

What is the current behavior?
When attempting to use raven-js in a ServiceWorker, Raven._makeRequest will fail because XMLHttpRequest is not available to SW environments.

What is the expected behavior?
Use the fetch api when available.

Which versions of Raven.js, and which browser and OS are affected by this issue?
All

Did this work in previous versions of Raven.js?
No

Are you using the CDN (http://ravenjs.com)?
No

Are you using hosted Sentry or on-premises?
Hosted

I put in a really quick hack into our /sw.js to make it work:

Raven._makeRequest = (opts) => {
  const auth = Object.keys(opts.auth).map((key) => `${key}=${opts.auth[key]}`).join('&');
  const headers = new Headers();
  headers.append('origin', self.location.origin);
  const req = new Request(`${opts.url}?${auth}`, {
    method: 'POST',
    body: new Blob([ JSON.stringify({ ...opts.data, ...opts.auth }, null, 2)], { type: 'application/json' }),
    mode: 'cors',
    credentials: 'omit',
    headers,
    referrer: self.location.origin
  });

  fetch(req);
}

[LewisJEllis]

Interesting, I was surprised to hear that there's an environment with fetch but not XHR, but after reading up on SW docs and this chromium issue on the XHR removal it makes sense.

I'll add this to the todos.

[mayfield]

Would love to have sentry in my ServiceWorkers. They tend to be a blackholes for errors otherwise.

[josketres]

I'd also like to have sentry in my ServiceWorkers!

[kamilogorek]

It won't fail anymore, but it also won't use fetch – https://github.com/getsentry/raven-js/blob/master/src/raven.js#L1805
I believe we can add fetch transport if it's available for that case, but it'll also mean handling it in all the places (promises vs. callbacks)

[austinpray]

Opened a little PR for this

[mayfield]

Another PR option that I'm using in my app already: #1156