When init.headers are native Headers, they won't get send

[FokkeZB]

When options.headers already is a native Headers object, this will lead to an empty this.headers:

cross-fetch/dist/browser-ponyfill.js

Lines 346 to 348 in 2257827

	if (options.headers || !this.headers) {
	this.headers = new Headers(options.headers);
	}

This is because the instanceof check here is done against the polyfil:

cross-fetch/dist/browser-ponyfill.js

Lines 93 to 96 in 2257827

	if (headers instanceof Headers) {
	headers.forEach(function(value, name) {
	this.append(name, value);
	}, this);

We should either not override Headers if it already exists, or keep a reference to the original and include it in the instanceof check as well.

[lquixada]

hey @FokkeZB ! Thanks for reporting that. cross-fetch is just a proxy for node-fetch on node environment and whatwg-fetch on browsers. The issue you're referring to is on the whatwg-fetch side. Please double check if this also happens on https://github.com/github/fetch/.

[FokkeZB]

Hey @lquixada - this is indeed happening there as well:

Sandbox: https://codesandbox.io/s/determined-cdn-7k3gx?file=/src/index.js
Live: https://7k3gx.csb.app/

[lquixada]

Hopefully they will handle this issue! Closing this one.

[FokkeZB]

Hope so! Reported at JakeChampion/fetch#860