How to make qualtrics pick up data from Javascript?

Hi All!
I have an Intercept and Survey where I defined Embedded Data I want to collect. It does show on the website. On the intercept, the Embedded Data value type is "Value from Javascript".
Having Survey URL I'm able to append query parameters into URL and the data is visible in the Survey Results (so it does work when I add query params manually).
Now I want to find a way to make Qualtrics read those values automatically from Javascript. Should those values be stored on global window object?
It's an single page application, to launch the survey popup I use a command: "QSI.API.run()".
The Embedded data example on intercept:
name: isSignedInUser | type: Value from Javascript | variableName: data.isSignedInUser