Function describeTrend

describeTrend(points: readonly PricePoint[]): PriceTrend

Summarize the latest price move for a series from its last two points. Returns a flat, zero-delta trend when there are fewer than two points.

Parameters

points: readonly PricePoint[]
The series points, ascending by time.

Returns PriceTrend

The direction, signed USD delta, and percent change of the last move.

Example

describeTrend([{ t: 1, usd: 20 }, { t: 2, usd: 22 }]);
// => { direction: "up", deltaUsd: 2, pctChange: 10 }

Source

export function describeTrend(points: readonly PricePoint[]): PriceTrend {
  if (points.length < 2) {
    return { direction: 'flat', deltaUsd: 0, pctChange: 0 };
  }
  const last = points[points.length - 1].usd;
  const prev = points[points.length - 2].usd;
  const deltaUsd = round2(last - prev);
  const pctChange = prev !== 0 ? (deltaUsd / prev) * 100 : 0;
  const direction: TrendDirection = deltaUsd > 0 ? 'up' : deltaUsd < 0 ? 'down' : 'flat';
  return { direction, deltaUsd, pctChange };
}