为什么我在Chrome中看不到我的HTTP标头？

Question

I am performing a fetch:

fetch(url, fetchOptions);

fetchOptions is configured like so:

var fetchOptions = {
  method: options.method,
  headers: getHeaders(),
  mode: 'no-cors',
  cache: 'no-cache',
};

function getHeaders() {
  var headers = new Headers(); // Headers is part of the fetch API.
  headers.append('User-ID', 'foo');
  return headers;
}

Checking fetchOptions at runtime it looks as follows:

fetchOptions.headers.keys().next() // Object {done: false, value: "user-id"}
fetchOptions.headers.values().next() // Object {done: false, value: "foo"}

But user-id is nowhere to be found in the request headers per Chrome dev tools:

GET /whatever?a=long_name&searchTerm=g HTTP/1.1
Host: host:8787
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
accept: application/json
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36
Referer: http://localhost:23900/
Accept-Encoding: gzip, deflate, sdch
Accept-Language: en-US,en;q=0.8,fr;q=0.6

Why can I not see my "User-ID" header in Chrome dev tools, and why does the header key appear to have been lowercased?

Answer 1

Incase someone else has a similar problem there were two possible culprits for this:

1. I might not have been starting Chrome with the correct flags.

The following didn't work when run from a Windows shortcut:

"C:\Program Files (x86)\Google\Chrome\Application\chrome.exe" -enable-precise-memory-info -disable-web-security

The following did work when run from a Windows command prompt:

C:\whatever\48.0.2564.82\application\chrome.exe  --disable-web-security --user-data-dir=C:\whatever\tmp\chrome 

2. The addition of no-cors to the mode of the request might have caused an OPTIONS request to precede the GET request and the server did not support OPTIONS.