Fetch event not receiving request headers

Question

It seems that fetch event inside service worker isn't receiving request headers, although it is stated in MDN documentation:

You can retrieve a lot of information about each request by calling parameters of the Request object returned by the FetchEvent:

event.request.url
event.request.method
event.request.headers
event.request.body

Code for fetching resource from main thread:

fetch(`${companyConfig.base}ticket-scanner/config`, {
    headers: {
        'X-Nsft-Locale' : `en`,
        'X-Nsft-Id': `1`,
    },
}).then((response) => {
    return response.json();
}).then((data) => {...})

Fetch event handler inside SW file:

self.addEventListener('fetch', function(event) {
  event.respondWith(
    caches.match(event.request, {cacheName : CACHE_NAME})
        .then(function(response) {
            if(response) {
                return response;
            }
            console.log(event.request.headers); //Log out headers
            return fetch(event.request).then(function(response){
                return response;
            }).catch(function(err){
                console.error(err);
            })
        })
    )
});

Logging headers for every fetch event gives me empty object:

Headers {}

This is preventing me to cache this specific request which requires only these two headers. Credentials aren't required. Am I missing something?

Answer 1

The Headers interface is iterable, supports a .get() accessor, and a .has() existence check.

You could take advantage of any of that to read the values you care about.

const request = new Request('https://example.com', {
  headers: {
    'x-header-1': 'header 1 value',
    'x-header-2': 'header 2 value',
  }
});

for (const [header, value] of request.headers) {
  console.log(`${header}: ${value} (via iterator)`);
}

console.log(`'x-header-1' is ${request.headers.get('x-header-1')}`);

console.log(`'x-header-2' ${request.headers.has('x-header-2') ? 'exists' : 'does not exist'}`);