JavaScript self-executing closure

JQuery is an obvious example of self-executing closures.
Javascript code
1. //Without parameters
2. (function(){
3. alert('hello');
4. })();
5.
6. //With parameters
7 . (function(name){
8. alert('Hello ' + name);
9. })('world');

What is the use of this closure? At first glance, it is surrounded by parentheses, and local variables cannot escape and cause trouble everywhere. This is one of its main uses. Of course, it is also indispensable for encapsulating some JavaScript libraries.