[z3t4]

Prior to ES6 JavaScript did not have async functions, just normal functions. Async functions came from the runtime, not JavaScript the language. For example there is no setTimeout function in JavaScript, it has to be implemented by the framework that runs the JavaScript. Talking about an function being async makes it confusing though. It's better to think of them as events. You call a function that executes a job, and specify a function to be called (an event handler) when the job has been completed. Putting the callback function in the function arguments is just a convention, other conventions are foo.on("ready") = handlerFunction; foo.ready = handlerFunction; foo.error = errorHandler; bar(handlerFunction); biz(successHandler, errorHandler); The callback convention is less verbose and probably why it's the most popular. Using just functions makes you more powerful...