var bs = require('bs-formula');

var inputs = {
  currentPrice: 57,         // current price of the underlying asset
  strikePrice: 50,          // strike price of the option
  interestRate: 0.01,       // annual risk-free interest rate
  volatility: 0.50,         // volatility of the underlying asset
  timeToExpiration: 0.25    // time to expiration of the option in years
};

bs(inputs); // 9.70