Question

I’ve been told a few times that it’s “bad” to use exceptions in javascript. Haven’t really been told why it’s bad, but inestead that I should use break, continue and return instead.

Which is fine, except I don’t need to return/break/continue, I need to throw. I have a case where I have iterator functions nested in each other, each one returns the next value on call, so I use an exception to indicate that there’s nothing more to iterate : seems like a logical way to do it, makes the code clean and works perfectly in practice. Is there really any reason not to use exceptions in js?

Second question, when I’m using exceptions, what kind of objects should I throw? For errors I’ll obviously throw instances of Error, but for special cases (stop iteration, etc) I needed a quick way to check for those specific exceptions, and what I did is simply define an empty named function (function StopIteration(){}) and since functions are compared by reference I can always check if it’s my special case or I should just rethrow. Is there a better or more idomatic way to do this in js? Should I really try to refactor my code avoid using exceptions?

Thank you

Answer 1

exception handling is in general slower than normal evaluation and only for exceptional situations

for stopping iterations you are better of defining a hasNext or isEmpty function for an ending condition or return a sentinel value (like undefined) when there are no more elements so the loop becomes

//with hasNext
while(it.hasNext()){
var val = it.next();
//...
}
//or with a sentinal undefined
while( (val = it.next()) !== undefined){
//...
}