Callback not provided pattern in NodeJS

Question

I usually write NodeJS code for hours, and there is a common situation I'm not sure how to face. Given the following async function call (where we forget the needed callback):

function foo (callback) {
    // Perform a task and call callback when finished
    callback();
}
foo(); // We forget the callback

Which is the better way to handle this? I find two options:

1. Make foo() function more robust adding this as the first line: callback = callback || function () {} callback = callback || function () {} .
2. Let it crash when foo() tries to call callback() and it does not exist.

Maybe a third option (which I prefer) would be the best one: throwing a custom error if the callback is not provided, as the first lines of foo() . For instance:

function foo (callback) {
    if (!callback) {
        throw new Error('No callback provided');
    }
    // More stuff here
    callback();
}

My question is: Is there any well-known patter to solve this situation? Which approach do you think is the better one? Do you solve this in a different way?

Answer 1

It all depends if your callback is mandatory or not.

• If it is mandatory then you should fail fast and do the throw new Error('No callback provided'); .

• If it is optional then the standard practice is that you just call it if it exists. Instead of creating a new function, just add a check in the place where it is gonna get called:

   if ( callback ) { callback(); } 

or in a single line:

callback && callback();