The ServiceWorkerGlobalScope.onsync event of the ServiceWorkerGlobalScope interface is fired whenever a SyncEvent event occurs. This is triggered when a call to SyncManager.register is made from a service worker client page. The attempt to sync is made either immediately if the network is available or as soon as the network becomes available.
ServiceWorkerGlobalScope.onsync = function(SyncEvent) { ... } self.addEventListener('sync', function(SyncEvent) { ... })
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
onsync | 
49  | 
79  | 
 44 
Extended Support Releases (ESR) before Firefox 78 ESR do not support service workers and the Push API. 
 | 
No  | 
24  | 
No  | 
49  | 
49  | 
44  | 
24  | 
No  | 
5.0  | 
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    https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerGlobalScope/onsync