Relative strength

// The chart's market against another, both rebased to 100 at the first bar they share: above
// 100 the chart's market has done better since then. Against ETH by default, so BTC and HYPE,
// the charts most often open, read against something else; on an ETH chart, or with "Chart" in
// the market setting, it compares the market with itself, a flat line at 100.
indicator('Relative strength', { shortName: 'RS', precision: 2 });

const against = input.market('Against', 'ETH');

const chart = bars();
const other = bars(against === null ? {} : { market: against });
const base = state.bar(na);

const ratio = plot.line('Relative strength', { width: 2 });
const par = plot.level('Par', 100, { style: 'dashed' });

chart.onBar(() => {
  if (isNa(other.close) || other.close === 0) return;
  const value = chart.close / other.close;
  if (isNa(base.value)) base.value = value;
  ratio.set((100 * value) / base.value);
});