Support for user-defined formatting of time values

Hi,

By setting tick formatters in ‘values’ in an axis, I can show timestamps in 24h format. But the selected “Time” is always printed in 12h format with am/pm. I would like to print that in 24h format as well.

I added an option ‘timeSeriesVal’, by changing this line in Line.js:

const _timeSeriesVal = timeSeriesVal(tzDate);

to:

const _timeSeriesVal = opts.timeSeriesVal ? opts.timeSeriesVal(tzDate) : timeSeriesVal(tzDate);

and with this I can pass my own formatting function. I’m not sure this is the right way to do it though; specifically I’m not sure the name of this option is correct / descriptive.

[leeoniya]

ok, series.value can now be a template string and will respect opts.tzDate.

let opts = {
  tzDate: ts => uPlot.tzDate(new Date(ts * 1e3), 'Europe/London'),
  series: [
    {
      value: "{YYYY}-{MM}-{DD} {HH}:{mm}:{ss}"
    }
  ]
}

[leeoniya]

closing this issue in favor of #87 to stay on topic. i’ve added some more thoughts/concerns there. let me know what you think.