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How Can This Unnamed Function Be Called?

I was reviewing the script provided by Facebook in order to run it's authorization. I ran into this puzzling bit of code:
(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_US/sdk.js";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));
As an unnamed function in its own scope, it would seem like this could never be called, but there it is, included in the boilerplate script.
What is going on here?

The function is an Immediatly Invoked Function Expression
(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_US/sdk.js";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));
If you notice the function has 3 arguments d, s, id then you will notice the function body.. At the end it calls it self passing in the args document, script, facebook-jssdk.
All this function does is creates a script such as.
<script id="facebook-jssdk" src="//connect.facebook.net/en_US/sdk.js"></script>
and inserts it before the first script tag in the document.

Display variable inside JavaScript

I want to change a hyperlink inside a script with a variable. It's the FB SDK, i want to display the SDK in the language the user chose on my website.
The variable is {$lang_fb} and returns the correct result (here:en_US) if I use it in normal php.
If I use the variable inside a script on a plain HTML page there is no result.
The script:
<script>
(function(d, s, id) {
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return;
js = d.createElement(s); js.id = id;
js.src = "//connect.facebook.net/{$lang_fb}/sdk.js#xfbml=1&version=v2.5&appId=01234567890";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));
<script>
results in the identical code in the page
What can I do?

If you are in a PHP script, you need to put the php tags or escape the string.
Way one
<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/<?php echo {$lang_fb} ?>/sdk.js#xfbml=1&version=v2.5&appId=01234567890";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
Way two
<script>(function(d, s, id) {
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return;
js = d.createElement(s); js.id = id;
js.src = "//connect.facebook.net/".{$lang_fb}."/sdk.js#xfbml=1&version=v2.5&appId=01234567890";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
If you don't share more code we can't view what happens.

The soluition:
js.src = "//connect.facebook.net/{/literal}{$lang_fb}{literal}/sdk.js#xfbml=1&version=v2.5&appId=1234567890";
Thanks for your help!!!

Since you are using a file extension, that is not PHP related, you need to setup php to process this extension.
For apache you can do this with the file .htaccess:
AddHandler application/x-httpd-php .tpl
Of course you also need to require the Facebook SDK which creates {$lang_fb}.

$lang_fb is a php variable and will not work in javascript. Are you embedding your script tag within php file? If yes then you can simply use the following:
<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/"+<?php echo $lang_fb; ?>+"/sdk.js#xfbml=1&version=v2.5&appId=01234567890";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));
</script>

Add parameters to a web widget

I'm building a simple web-widget similar to Facebook Like button, and I want to set some parameters(ex. websiteId) to use them in my dynamically added script(http://analytics.dev/bundles/andreistatistics/js/like-button.js).
My question is: is there a way to pass my param websiteId to use it in like-button.js file? I would also like to avoid conflicts with other wbesiteId params defined in DOM.
<div class="like-button-container"></div>
<script>
(function(d, s, id) {
var websiteId = 7;
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id))
return;
js = d.createElement(s);
js.id = id;
js.src = "http://analytics.dev/bundles/andreistatistics/js/like-button.js";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'my-like-button'));
</script>

Validation failed because of a single character in Facebook Connect code

I am trying to use some Facebook code in one of my pages.
The code is:
<script type="text/javascript">(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_US/all.js#xfbml=1&appId=000000000";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
However when I try to validate this as an XHTML+RDFa page I get an error. The error is caused by the & sign in this part "xfbml=1&appId". The WC3 validator recommends using:
&
even in urls it says.
However, when I change the ampersand sign to:
&
The script no longer works.
Is there a way to get this to work correctly and still validate?

You should be able to get it to validate by wrapping the code in a CDATA tag, like so:
<script type="text/javascript">(function(d, s, id) {
//<![CDATA[
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_US/all.js#xfbml=1&appId=000000000";
fjs.parentNode.insertBefore(js, fjs);
//]]>
}(document, 'script', 'facebook-jssdk'));</script>

<script type="text/javascript">
/*<![CDATA[*//*---->*/
(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_US/all.js#xfbml=1&appId=000000000";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));
/*--*//*]]>*/
</script>
Much of JavaScript will not be interpreted correctly by the XHTML parser. You need to escape it with CDATA.

How to catch a 403 forbidden error in JS?

I am trying to hack a little this facebook javascript code to make a call on an other js if the GET failed.
I have something like this :
<div id="fb-root"></div>
<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/yi_YI/all.js#xfbml=1&appId=###";
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
<div class="fb-comments" data-href="###" data-num-posts="10" data-width="646"></div>
Which give a 403 Forbidden (/* Not a valid locale. */). When it does something like this, I want to be able to load the en_US facebook sdk. So, I have tried :
<div id="fb-root"></div>
<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/yi_YI/all.js#xfbml=1&appId=###";
try { fjs.parentNode.insertBefore(js, fjs); }
catch(err) {
js.src = "//connect.facebook.net/en_US/all.js#xfbml=1&appId=###";
fjs.parentNode.insertBefore(js, fjs);
}
}(document, 'script', 'facebook-jssdk'));</script>
<div class="fb-comments" data-href="###" data-num-posts="10" data-width="646"></div>
But, it doesn't work, keep getting 403 Forbidden, like if the try and catch(err) is not working.

You can't get the HTTP response status of a cross-domain request.
The reason you're getting a 403 is because Facebook doesn't support yi_YI as a locale – you will always get a 403. The locale you request must be on the list of supported locales.

use onerror method for script:
<div id="fb-root"></div>
<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/yi_YI/all.js#xfbml=1&appId=###";
//handle loading error
js.onerror = function(){alert("script loading error")};
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>
<div class="fb-comments" data-href="###" data-num-posts="10" data-width="646"></div>