Adding a note about "initialized" event and track() callback

[prigiattiperrut]

Proposed changes

1. Added clarification on detecting when Analytics.js has loaded:

• Instead of relying on the ready() method, users can listen for the initialize event (window.analytics.initialized). This event returns true even when a destination is blocked, providing a more reliable way to detect library loading.

2. Updated function behavior after a 300 ms timeout:

• Clarified that the function, which runs after a 300 ms delay to give the browser time to make outbound requests, may not execute if one of the device-mode libraries is blocked from loading.

Merge timing

ASAP once approved

[github-actions]

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[JohnMealy23]

I'm confused by this line. Generally when the terms "listen", "emit" and "event" are used, it's in reference to a pubsub system. Such a system would be ideal. Something like...

window.analytics.on('initialized', function(event, properties, options) {
  console.log(event, properties, options)
});

However, I'm not seeing any way of subscribing here. To date, window.analytics.initialized is a single boolean value. The only way I can see to "listen" to it would be to set up an interval that poles for the value to change. This is do-able (albeit inelegant, IMO).

If I'm correct, and there is no way of subscribing to changes in window.analytics.initialized, I'd strongly suggest updating this doc for clarity. And if there is a way of subscribing, I'd suggest linking to that documentation here.

[prigiattiperrut]

Hey @JohnMealy23, thanks for your note! I've created a new PR to address the adjustment:
https://github.com/segmentio/segment-docs/pull/7036/files