Would an _.if function be useful?

_.if would take two arguments, a primary function and a conditional function. It would return a new function that, when called, will call the primary function only if the conditional (called with the same arguments) returns a truthy value. It would look something like this:

_.if = function(func, condition){
    return function(){
        if (condition.apply(this, arguments)){
            return func.apply(this, arguments);
        }
    }
};

This way you can write generic functions and then easily add conditions for execution when passing them to iterators. Something like:

items.forEach(_(processItem).if(isNotProcessed));

Would this be a useful addition?

No file, test, or entry point is named. Start by reviewing existing function utilities and iterator-related APIs in the repository, then assess whether the proposed _.if behavior has clear acceptance criteria. Done would require a maintainer decision plus implementation and tests, none of which the issue specifies.