[BUG] address issues #1517 add unload listener and #1524 config from snippet

[xiao-lix]

1. Add event listener on unload event to address [BUG] addHousekeepingBeforeUnload should also be listening to the 'unload' event #1517
2. Add to initialize config items to address [BUG] Config items are not functional for current snippet disableFlushOnBeforeUnload, disableFlushOnBeforeUnload and maybe others #1524
3. Add to initialize correlationHeaderExcludePatterns config item in ajax.ts to address [BUG] correlationHeaderExcludePatterns is not honored in Ajax calls #1528

[MSNev]

Why are we doing all of these?

Setting the defaults for lines 79, 80 and 82 I get as they are not provided otherwise, but the other checks to "set" the existing value strictly to a boolean or like on line 88 to the same value doesn't seem right...

It is also really bad from a minification perspective as all of the long names on the config elements can't be compressed.

[MSNev]

ok, just went and looked at the bug and the implementation...
As the usage within the code iterates over the list of "keys" on the object returned by getDefaultConfig(), this sort of works -- it's just not very nice.

This is also very prone to breakage whenever we add a new config to IConfiguration -- if we don't remember about this of forget...

I think we need to rethink this pattern as the ctx.getConfig(identifier, field, value) does a couple of things that makes this a non-trival change as it looks up both the root config and the extensionConfig for the identifier...

[MSNev]

Ok, so this line _self.config = ctx.getExtCfg<IConfig>(identifier) (Line 498 on my repo) deals with the "identifier" version of things as this will just return those values.... So it's just the root level ones that we are interested in that are getting missed (which is what the default stuff is effectively doing)...

I'm wondering whether we can do something really simple like... (_assignFn comes form the shims)
_self.config = __assignFn(ApplicationInsights.getDefaultConfig(), config, ctx.getExtCfg<IConfig>(identifier));

This effectively creates a new object using the combination of the 3 arguments, where the last value wins.
Internally, this is effectively the Object.assign() function, if you want to look it up.

We should still set the default values (lines 79, 80 and 82) so that they are set correctly, but the rest (I think) then won't be required.

[xiao-lix]

@MSNev Sorry Nev for the confusion... I see what's going on here.

For other configurations I added before, they're not analytics extension related and should not bring in here.

maxBatchSizeInBytes, maxBatchInterval, isBeaconApiDisabled, enableSessionStorageBuffer, isRetryDisabled, disableTelemetry are sender config and initialized here. And when user passes in user defined config, it receives here.

maxAjaxCallsPerView , disableCorrelationHeaders, enableCorsCorrelation, correlationHeaderExcludedDomains, disableAjaxTracking are remote dependency extension config , initialized here and received user defined here.

And disableCookiesUsage is handled by the cookie manager you created.

But for the above three configs, this is the place to initialize them. And on line 505, getDefaultConfig is missing the param config so the user defined configs dropped!

I think we need this config.[key] pattern because we don't need all keys from config, like "extensionConfig" is in config object too but we only need to initialize some of the configs... does that make sense?