Thx for the clarification,
I found that using #asset on the "jsreport-client", needed to be modify the config in the jsreportapp (PORT:5488 one) called "jsreport.config.json".
Then, declaring the the assets option like jan_blaha said.
And most importantly, the asset should be on the 5488 port app assets folder, rather than creating an assets folder and put that in your project.
E.G.
connecting to
http://example.com:5488
in the GUI, click the "+" sign next to the assets folder
select your asset to be uploaded.
rename to what your project code point to ( like... {#asset myFileName.myExtension @encoding=dataURI} should name your asset name as: myFileName.myExtension)
I dun know if this is the correct approach, but this should work fine.
Maybe the assets document need to elaborate for more and the jsreport-client should write more about the assets too.
Seems that the assets function are a newly item to the jsreport