[BUG] Telemetry Buffer Getting Cleared in Offline Mode - Online Status Incorrectly Initialized in Offline Listener

[davesauce14]

Behavior

In the scenario for progressive webapps the telemetry buffer is not being preserved during offline mode.

Culprit

This is happening because, in the constructor for OnlineListener, we initialize _onlineStatus = true.
Which prevents the Sender._xhrReadyStateChange event handler from adding it back to the telem buffer after failure.

ApplicationInsights-JS/channels/applicationinsights-channel-js/src/Offline.ts

Line 17 in 22d3787

let _onlineStatus: boolean = true;

ApplicationInsights-JS/channels/applicationinsights-channel-js/src/Sender.ts

Line 387 in 22d3787

} else if (Offline.isOffline()) { // offline

This logic will be sufficent in most scenarios since the initial GET request, would have to have been fetched over the wire for application insights to have been invoked.
But in the case of PWAs we would have this cached, and initialization would happen, even though we are offline.
Initializing to true is not sufficient.

Additional notes

The hooks for detecting network changes: online and offline are working successfully, I have tested these!
But that will only re-evaluate the _onlineStatus if the status of the network has changed, after the application was loaded, which may not be the case

Suggested Fix

Initialize _onlineStatus by evaulating the status of the network, using a browser hook such as window.navigator.online

Steps to recreate

Open a PWA when the application is in offline mode.
You will see that OfflineListener._onlineStatus is true and telemetry buffer is not being preserved.

[MSNev]

v2.6.2 is now fully deployed

[github-actions]

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