javascript - getSubscription upon activation of sw -

i'm not sure i'm making mistake.

i want register service worker , moment it's "activated" make xhr request server in order store subscription data.

self.addeventlistener('activate', function(event) {     console.log('activated', event);     event.waituntil(          self.registration.pushmanager.getsubscription().then(function (subscription) {          console.log(subscription);//this null          })     ) }) 

so far wasn't able subscription inside sw, can other javascript on site. not udnerstanding?

edit:

this how register pushmanager

function reg(){    if ('serviceworker' in navigator) {      navigator.serviceworker.register(sw).then(function(reg) {          reg.pushmanager.subscribe({             uservisibleonly: true         }).then(function(subscription) {             send_subscription(subscription);         });      }).catch(function(error) {         console.log(':^(', error);     });   } }  function send_subscription(subscription){ [...] } 

you attempting subscription pushmanager:

the pushmanager.getsubscription() method of pushmanager interface retrieves existing push subscription.

if intended, first have subscribe pushmanager using pushmanager.subscribe().