let u;

const ws = new WebSocket("ws://127.0.0.1:6789/");

ws.onmessage = function(event) {
    const data = JSON.parse(event.data);

    switch (data.type) {                   
        case 'ohlc':
            let ohlc = [data.ts, data.o, data.h, data.l, data.c];

            if (u == null)
                u = new uPlot(opts, ohlc, document.body);
            else
                u.setData(ohlc);                  
            break;
        case 'askbid':                   
            break;
        default:
            console.error("unsupported event", data);
    }
};