Usually, IIFEs are used to create a scoping context, i.e. a context in which all variables and function definitions are scoped within. This allowed to create a »shield« under which the functions and variables aren’t visible externally or globally outside of the wrapped function.
An IIFE can be written both with the calling brackets (i.e. ()) on the outside or the calling brackets inside of the wrapping brackets
(() => {
// Do something
})();
(() => {
// Do something
}());
While it’s quite common to write IIFEs anonymously (i.e. without a function name), named IIFEs are also possible.
(function something() {
// Do something
})();