fetch("https://httpstat.us/200", { method: "HEAD" }).then(response => console.log(response.body))

fetch("https://httpstat.us/204").then(response => console.log(response.body))

Deno does this correctly:

/m/s/P/g/denoland ❯❯❯ deno
Deno 1.18.2
exit using ctrl+d or close()
> fetch("https://httpstat.us/200", { method: "HEAD" }).then(response => console.log(response.body))

Promise { <pending> }
> null
> fetch("https://httpstat.us/204").then(response => console.log(response.body))

Promise { <pending> }
> null

This is the only related test I can find right now:

test(function() {
  var response = new Response(null, {status: 204});
  assert_equals(response.body, null);
}, "Testing null Response body");

oh and this:

var nullBodyStatus = [204, 205, 304];
nullBodyStatus.forEach(function(status) {
  test(function() {
    assert_throws_js(TypeError,
      function() { new Response("body", {"status" : status }); },
      "Expect TypeError exception ");
  },"Throws TypeError when building a response with body and a body status of " + status);
});