I wonder what went wrong, and where we call the monkey-patched Promise.prototype.then.

This [0] doesn't seem to be it, because V8's v8::Promise::Then should be using the original builtin.

Kentaro or Domenic, could you help triage?

[0] https://cs.chromium.org/chromium/src/third_party/WebKit/Source/bindings/core/v8/ScriptPromise.cpp?l=238&rcl=71ccd71cf4cea51efacfdbe543e66ecff171fca2

ScriptPromise::Then is not related. The behavior comes from v8::Promise defined in v8.h.

I'll take a look when I'm in office tomorrow. I was under the impression that v8::Promise::Then [0] would use the untampered version of the builtin.

https://cs.chromium.org/chromium/src/v8/src/api.cc?l=7453&rcl=1245787434f94365412645d9530ad60212128586

I don't understand the issue here. Given this code:

  Promise.prototype.then = ()=>{};
  fetch("y18.gif").then(r => console.log(r))

line two's `.then(...)` calls the no-op function declared in line one. So yeah, definitely nothing will get output.

This seems completely working as intended. The internal implementation of fetch is working fine still. (You can also check the network tab to confirm that the resource is still fetched.) But the promise returned is still a Promise, that uses Promise.prototype, and thus calling `.then()` on it will do nothing if you've explicitly set `Promise.prototype.then` to a no-op.

Argh. I'm being an idiot and totally overlooked that part. Thanks!