Question

So I started learning javacript and I’ve noticed that the coding convention for functions and callbacks is something like this (this is a jQuery example but I’ve seen these everywhere):

$.getJSON('some/url.json', function(a) {
// do stuff with a here
});

Coming from other languages, I would usually write the above as this:

function myFunction(myVar){
//do stuff with myVar here
};

$.getJSON('some/url.json', myFunction());

Why is the former usually the preferred way of writing in JS, instead of the [probably more readable] latter?

Answer 1

There are plenty of good reasons to use the second, more explicit, format (assuming you fix the issue listed in the comment), including:

• reusing the function passed as a callback
• giving that function a definitive name to make it easier to debug
• making sure that function is noted as something important in your system
• separating out that functions because it’s simply too long to comfortably declare in place

But the first format, with an anonymous function passed as a callback is short and sweet. If you don’t need to reuse the function, if it’s relatively short, and if it’s not of high importance in your system, it can be really useful to declare it exactly where you use it. You avoid adding another variable to your scope, and you make it entirely clear exactly what that function is for.