Use js onload on body with a Ticker

I use some data from navitia api (store in a database) and try to display them on Xibo. It’s for arrivals and departures time. But the trouble is that my hours are like “20190509T135300” and I just want to be displayed like “13:53”. I tried to make an onload function in js but I haven’t be able to make anything with it. Is it possible? Can i manage my data in the database directly?

My xibo is in 1.8.12.

I have some small basic knowledge on js but even if i try some internet exemple it didn’t work.

Thanks in advance for yours concerns

I up my topic, didn’t find any solution yet. Will be very thankful if anyone have idea to help me.