I am familiar with http status codes, but recently I saw a strange line in my chrome debugger. Instead of ordinary Status Code:200 OK
I saw the following: Status Code:200 OK (from ServiceWorker)
.
My guess is that this just tells me that ServiceWorker is somehow responsible for accessing this document, but this is just random guess. Can anyone authoritatively (without guesses, with links to respected resources) tell me what does this mean and what are the implications?
To access this feature in Chrome, simply open the developer tools (command-option-I or command-option-J on a Mac) and select the Network option from the drop-down menu at the top.
The Network view allows you to see and analyze the network requests that make up each individual page load within a single user's session. You can use this view to investigate the causes of slow pages and identify performance bugs.
Right click -> inspect -> then you will have the chrome dev tools just by selecting networks you can filter what's the browser is loading also you can see the http request going through your application.
Just click the Response tab, which is to the right of the Headers tab that's open in your screenshot.
This is a common source of confusion, so I wanted to go into a bit more detail.
I have a full working demo in this Gist, and you can view a live version of it thanks to RawGit.
Here's the relevant portion of the service worker code inline, for illustrative purposes:
self.addEventListener('fetch', event => {
if (event.request.url.endsWith('one.js')) {
// Requests for one.js will result in the SW firing off a fetch() request,
// which will be reflected in the DevTools Network panel.
event.respondWith(fetch(event.request));
} else if (event.request.url.endsWith('two.js')) {
// Requests for two.js will result in the SW constructing a new Response object,
// so there won't be an additional network request in the DevTools Network panel.
event.respondWith(new Response('// no-op'));
}
// Requests for anything else won't trigger event.respondWith(), so there won't be
// any SW interaction reflected in the DevTools Network panel.
});
And here's what a filtered version of the Network panel looks like in Chrome 48 when that service worker is in control of a page, and requests are made for one.js
, two.js
, and three.js
:
Our service worker's fetch
handler will do one of three things:
one.js
, it will fire off a fetch()
request for the same URL, and then call event.respondWith()
using that response. The first one.js
entry in the screenshot, the one with "(from ServiceWorker)" in the "Size" column, is there by virtue of the fact that we called event.respondWith()
inside the fetch
handler. The second one.js
entry in the screenshot, the one with the little gear icon next to it and "(from cache)" in the "Size" column, represents that fetch()
request that was made inside the service worker while responding to the event. Since the actual one.js
file was already in the HTTP cache at the point I took this screenshot, you see "(from cache)", but if the HTTP cache didn't have that response already, you would see an actual network request along with the response size.two.js
, it will handle the request by constructing a new Response
object "from thin air". (Yes, you can do that!) In this case, we are calling event.respondWith()
, so there's an entry for two.js
with "(from ServiceWorker)" in the "Size" column. But unlike with one.js
, we're not using fetch()
to populate the response, so there's no additional entry in the Network panel for two.js
.three.js
, our service worker's fetch
event handler won't actually call event.respondWith()
. From the perspective of the page, and also from the perspective of the Network panel, there's no service worker involvement with that request, which is why there's just a "(from cache)" rather than "(from ServiceWorker)" in the "Size" column.A service worker is a script that is run by your browser in the background. So Status Code:200 OK (from ServiceWorker) mean that “OK” success code, for GET or HEAD request and this status come from ServiceWorker.
You can read this link to understand more about this. http://www.html5rocks.com/en/tutorials/service-worker/introduction/
This is normal . To avoid confusion arising out by 200
for every request. Its showing that the request is a SUCCESS
but service-worker
has responded for the resource / request instead of network/server
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