A callback is a conventional approach to providing a way to hook into asynchronous tasks. A callback is simply a function that is passed to another function and is expected to be called at some later point, possibly immediately, possibility soon, and possibly never. Consider the following requestData function:
function requestData(path, callback) { // (Implementation of requestData)}
As you can see, it accepts a callback as its second argument. When calling requestData, the callback will typically be anonymously passed inline, like so:
requestData('/data/123', (response) => { /* ... */ });
It is, of course, totally fine to have previously declared the callback, and doing so can aid comprehensibility as now the reader of your code ...
