Calculations

Function contract

Source must define function calculate(params) and return a non-empty array of number or string values. Single-value table cells show the last array element.

function calculate(params) {
  // params: CalculationParams
  console.log('trade count', params.trades.length);
  return [params.trades.length];
}

Params object

calculate receives a CalculationParams object. There is no side field — the performance tab filters long/short/all trades and passes the subset as params.trades.

interface CalculationParams {
  capital: number;
  trades: Trade[];
}

interface Trade {
  id: string; // uuid
  userId: string;
  sessionId: string;
  tradeNumber: number;
  symbol: string;
  direction: 'long' | 'short';
  positionSize: number;
  entryPrice: number;
  openedAt: string; // ISO 8601 UTC
  /** Omit while the position is still open. */
  exitPrice?: number;
  closedAt?: string;
  profitLoss?: number;
  note?: string;
  tags?: string[];
  entryMethod?: string;
  exitMethod?: string;
  stopLoss?: number;
  takeProfit?: number;
  favorableExcursion?: number;
  adverseExcursion?: number;
  timeframe?: string;
  createdAt: string;
  updatedAt: string;
  messages?: Array<{ id: string; content?: string; createdAt: string }>;
}

Debugging with logs

In the calculation form tester, use console.log, console.warn, or console.error. Captured lines appear in a Logs section under the result (they are not shown on the session performance table).

Prefer console for debug output. You can also put intermediate strings in the return array — the performance table still displays only the last element:

function calculate(params) {
  var closed = (params.trades || []).filter(function (t) {
    return typeof t.profitLoss === 'number';
  });
  // last value is the cell display; earlier strings are visible in the tester Result JSON
  return ['closed=' + closed.length, closed.length];
}

Errors and timeout

Thrown errors become { ok: false, error: "…" }. Invalid returns use Invalid return type. Runs that exceed your timeout (Settings → Preferences, default 5000 ms) are killed and return Calculation timed out.