Make tracking several site IDs easier to users implementing Piwik using Asynchronous javascript

[mattab]

It is a common use case to want to track the data in two different websites in Piwik, for example one website for the current website and another one for the "aggregate" websites collecting data across several domains.

In this case here is the recommended practise: http://developer.piwik.org/api-reference/tracking-javascript#multiple-piwik-trackers

Note: When using multiple trackers, you must use the synchronous Javascript tracker object (ie. this will not work with the asynchronous tag).

The goal of this ticket is to remove this bracket from the documentation: '(ie. this will not work with the asynchronous tag)' and make it work when calling .push( 'setSiteId', X ) with X and Y.

This will also resolve a few support issues as this question occurs fairly often!

[tsteur]

Isn't there already a setSiteId method? What exactly is to do here?
Otherwise another solution would be to make it possible to use two trackers when using async

[tsteur]

Found the problem in current implementation, it always calls all setSiteId methods first... So we can either fix this or make two trackers work in async mode by using callback methods

[mattab]

Maybe proper solution is to throw an exception when setSiteId is pushed more than once?

[tsteur]

In 743ec5b: refs #5049 log to console (if exist) if methods, that are applied first, are registered multiple times. We do not throw an error as this would prevent script execution

[tsteur]

In a9d8533: refs #5049 fix tracker tests, jslint was not as happy as I was

[tsteur]

In 7c2dd6a: refs #5049 added possiblity to use async + multiple piwik trackers