Question

what’s the difference between a jQuery function

$.FunctionName = function(){ alert('Hello!') }

and normal javascript function?

function FunctionName(){ alert('Hello!') }

Answer 1

The former becomes a static method of the jQuery object.
The latter becomes just a regular function.

The only difference, really is the owner of the function. The jQuery object/constructor owns the first method, while the window object owns the second method, assuming it wasn’t defined in another function scope.

Generally, you do not usually do the first one unless you want to attach a specific method that’s related to jQuery. If you have a custom application specific function do the latter.