ACDL eventing with getState registered late

acdl-test2.js

// In a browswer window with URL about:blank
// Open the JS console and paste this code

window.adobeDataLayer =  [];

adobeDataLayer.push({
    x: 1
});
adobeDataLayer.push({
    event: "test",
    y: "a"
});
adobeDataLayer.push({
    x: 2
});
adobeDataLayer.push({
    event: "test",
    y: "b"
});

adobeDataLayer.push(function (dl) {
    dl.addEventListener("test", function() {
        console.log(dl.getState());
    });
});

var scriptElement = document.createElement('script');
scriptElement.src = "https://unpkg.com/@adobe/[email protected]/dist/adobe-client-data-layer.js";
document.body.append(scriptElement);

// Console output will be:
// {x: 2, y: "b"}
// {x: 2, y: "b"}

See how getState in the event handler returns the state after everything has been executed, because it has been registered too late.

How the data layer works for event that are registered late cannot really be different, because the state has already been computed with all previous pushes.

You can disable the event handling for past events and only get future events (see [addEventListener](https://github.com/adobe/adobe-client-data-layer/wiki#addeventlistener) and options.scope parameter). But if you register for past events (which is the default), then knowing how the state was previously would the data layer to either require to memorize how the state was at very step (with a huge memory impact), or to recompute every past step when registering events that listens for past events (with a huge performance impact).