Why is the facebook script include overcomplicated? - facebook

Question

The documentation for the Facebook like button suggests including the following script:
<script>(function(d, s, id) {
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return;
js = d.createElement(s); js.id = id;
js.src = "//connect.facebook.net/en_GB/all.js#xfbml=1";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
As I read it, this does nothing more than add the external all.js file before the first script tag on the page.
<script id="facebook-jssdk" src="//connect.facebook.net/nl_NL/all.js#xfbml=1"></script>
Is there any reason to not just add the completed script tag to the page source in the first place?

Answer 1

From the Javascript SDK page;
This code loads the SDK asynchronously so it does not block loading other elements of your page.
In other words, yes, you could most likely include it right away, but the user would experience it as if your page were loading more slowly.

Answer 2

What is the difference between this:
<script>(function(d, s, id) {
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return;
js = d.createElement(s); js.id = id;
js.src = "//connect.facebook.net/en_GB/all.js#xfbml=1";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
and this:
<script src="//connect.facebook.net/nl_NL/all.js#xfbml=1" async></script>
?