Question

Just by seeing what I’ve wrote now, I can see that one is much smaller, so in terms of code golf Option 2 is the better bet, but as far as which is cleaner, I prefer Option 1. I would really love the community’s input on this.

Option 1

something_async({
    success: function(data) {
        console.log(data);
    },
    error: function(error) {
        console.log(error);
    }
});

Option 2

something_async(function(error,data){
    if(error){
        console.log(error);
    }else{
        console.log(data);
    }
});

Answer 1

Many people will find option#1 easier to read and to maintain – two different callback functions for two different purposes. It is commonly used by all Promise Libraries, where two arguments will be passed. Of course, the question Multiple arguments vs. options object is independent from that (while the object is useful in jQuery.ajax, it doesn’t make sense for promise.then).

However, option#2 is Node.js convention (see also NodeGuide) and used in many libraries that are influenced by it, for example famous async.js. However, this convention is discussable, top google results I found are WekeRoad: NodeJS Callback Conventions and Stackoverflow: What is the suggested callback style for Node.js libraries?.

The reason for the single callback function with an error argument is that it always reminds the developer to handle errors, which is especially important in serverside applications. Many beginners at clientside ajax functions don’t care forget about error handling for example, asking themselves why the success callback doesn’t get invoked. On the other hand, promises with then-chaining are based on the optionality of error callbacks, propagating them to the next level – of course it still needs to be catched there.