Passing arguments in anonymous functions in JavaScript

Question

Sometimes I see JavaScript that is written with an argument provided that already has a set value or is an object with methods. Take this jQuery example for instance:

Answer 1

To me, this looks like were passing a function to the createServer function with two arguments that have methods already attached to them.

No. They were passing a function to createServer that takes two arguments. Those functions will later be called with whatever argument the caller puts in. e.g.:

function caller(otherFunction) {
     otherFunction(2);
 }
caller(function(x) {
    console.log(x); 
});

Will print 2.

More advanced, if this isn't what you want you can use the bind method belong to all functions, which will create a new function with specified arguments already bound. e.g.:

caller(function(x) {
    console.log(x);
}.bind(null, 3);
});

Will now print 3, and the argument 2 passed to the anonymous function will become an unused and unnamed argument.

Anyway, that is a dense example; please check the linked documentation for bind to understand how binding works better.