function betBlocked(v) {
  return (v === null || this.line_blocked);
}

function convertWin12(line) {
  return ["WIN__P1", "WIN__P2"].map((bet, i) => buildFactor(bet, line.V[i], betBlocked(line.V[i])));
}

function getConverterFn(line) {
  if (line.idTipMarket === 491) return convertWin12;
  //...
}

lines.forEach(line => {
  const factors = {};

  const converterFn = getConverterFn(line);
  if (converterFn) {
    converterFn(line).forEach(f => {
      factors[f.bet] = f;
    });
  }

  return factors;
});