Hi this is the cross-fetch author. In order to keep maximum consistency between node-fetch, whatwg-fetch and native browser fetch, I'm running the same suite of tests across all these implementations. For the 3.0.0-beta.9 version, there are only two issues with Headers' forEach method that differs from browsers' fetch and whatwg-fetch:

1. It does not accept thisArg as the second parameter
2. The callback does not provide a third argument: the header object itself.

Here's a code to illustrate that:

const headers = new Headers()
headers.append('Accept', 'application/json')

const obj = {}
const results = []
headers.forEach(function (value, key, object) {
  results.push({ value, key, object, thisArg: this })
}, obj);

console.log(results[0].object === headers) // true on browser, false on node-fetch 3.0.0-beta.9
console.log(results[0].thisArg === obj) // true on browser, false on node-fetch 3.0.0-beta.9

I realize that on version 2.6.1, it used to have both features. So my question: is this intentional? If not, does anyone mind if I open a PR?