Hey, I hope you鈥檙e the one who created st_echarts events function unable to reference chart object 路 Issue #48 路 andfanilo/streamlit-echarts (github.com) 
we can track the conversation there!
Right now I don鈥檛 think that鈥檚 possible, but I haven鈥檛 tried on my side. What happens if you write this instead of myChart ?
Also I think the series data and index are located in params, reading from Event and Action - Concepts - Handbook - Apache ECharts. I haven鈥檛 tried but does
function(params) { console.log(params.data); }
give back the series data? I鈥檓 not sure you鈥檒l get the active state in there but hopefully it does appear.