Embarking on Adventures in the Land of Logic It’s time for callback functions. What is a callback function? It’s just a function that’s passed as an argument to another function and is then executed inside the other function. I think it’s time to go through this concept in excruciating detail to put this behind us once and for all. We’ll cover passing anonymous functions (closures) and arrow functions as arguments to other functions, and then calling them too. Callback functions make a lot of sense in asynchronous languages since we may not want two functions to compete for finishing times.