A function to calculate the profit probability of an iron butterfly option strategy could be written as follows:

```
function ironButterflyProfitProbability(stockPrice, strikePrice, upperBreakeven, lowerBreakeven) {
if (stockPrice > upperBreakeven) {
return 1.0;
} else if (stockPrice < lowerBreakeven) {
return 0.0;
} else if (stockPrice > strikePrice) {
return (stockPrice - lowerBreakeven) / (upperBreakeven - lowerBreakeven);
} else {
return (upperBreakeven - stockPrice) / (upperBreakeven - lowerBreakeven);
}
}
//
function ironButterflyBreakevens(stockPrice, longCallStrikePrice, shortCallStrikePrice, longPutStrikePrice) {
var upperBreakeven = longCallStrikePrice + shortCallStrikePrice - stockPrice;
var lowerBreakeven = longPutStrikePrice - shortCallStrikePrice + stockPrice;
return [upperBreakeven, lowerBreakeven];
}
```

This function calculates the profit probability of an iron butterfly option strategy based on the current stock price, the strike price of the options, and the upper and lower breakeven prices of the strategy.

The function returns a probability value between 0 and 1, where 0 indicates that the strategy will not be profitable and 1 indicates that the strategy will be profitable. The function uses the current stock price, the strike price, and the upper and lower breakeven prices to determine the profit probability of the strategy.

For example, if the current stock price is $50, the strike price is $45, and the upper and lower breakeven prices are $55 and $35, respectively, the function would return a profit probability of 0.5, indicating that the strategy has a 50% chance of being profitable.

It is important to note that the calculations and examples provided above are for illustrative purposes only and do not constitute investment advice. The profit probability of an iron butterfly option strategy will depend on a variety of factors, including the volatility of the underlying stock, the time remaining until expiration, and other market conditions. You should consult with a financial advisor or conduct your own research before making any investment decisions.