javascript - What's the role of the parentheses in the following piece of code?

Question

This is the tracking code for Google Analytics:

var _gaq = _gaq || [];
_gaq.push(["_setAccount", "UA-256257-21"]);
_gaq.push(["_trackPageview"]);

(function() {
var ga = document.createElement("script"); ga.type = "text/javascript"; ga.async = true;
ga.src = ("https:" == document.location.protocol ? "https://ssl" : "http://www") + ".google-analytics.com/ga.js";
var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(ga, s);
})();

You can see that the function is inside parentheses.

Why do you think is that?

Answer 1

It is an anonymous function that is defined and invoked immediately. It cannot be invoked from the outside as it has no name. All the variables inside will be scoped to the anonymous function. This could be used to do some processing on the global scope without adding new members to it.