ABSTRACT
JavaScript relies heavily on callback functions: Instead of a function giving us a result immediately, we give it another function that tells it what to do next. Many other languages use them as well, but JavaScript is often the first place that programmers with data science backgrounds encounter them. In order to understand how they work and how to use them, we must first understand what actually happens when functions are defined and called. JavaScript allocates a block of memory big enough to store several instructions, translates the text of the function into instructions, and stores a reference to those instructions in the variable oneMore. The call stack allows us to write and call functions without worrying about whether we’re accidentally going to refer to the wrong variable. And since functions are just another kind of data, we can pass one function into another.
