How target reads data elements from launch that are passed as Mbox parameters?

[JyotiSharmaV]

I want to understand how Adobe Target reads the digital data layer. From one of my experiences, I was trying to pass page title from a data layer

While I used reading via javascript variable it did not work for me:

However, reading it as a core attribute worked

Why this is the case?

Also, I have pages with multi-product categories and they get passed into my data layer in the form of an array, and through JS code I am already successfully reading it via data element into eVars for my analysis. However, when I am trying to map this multi-product categories data element to user.categoryId to pass it as a Target mbox parameter for every page load nothing comes up in my favorite categories. Any suggestions as to why? This is why I am wondering how to read values out of the digital data layer into data elements for Target?

[alexbishop · Accepted solution]

Both data element examples you provided should work in theory. Worth pointing out that Page Info > Title is reading from document.title and your other example is reading from your data layer, so that raises a question of whether that data layer property is correct and/or populated as expected.

In terms of passing category IDs, how are you passing those values into Target? The most common way is to pass an mbox parameter called user.categoryId; and when passing multiple IDs then it should be comma-separated e.g.
"trousers,shoes,hats"