How popular is JavaScript?

It has gained lot of popularity because of the many libraries developed such as jQuery, Bootstrap, Node.JS, Win.JS, dojo etc. Together with HTML5 it has become all the more popular for web development.

The popularity of a programming language is described by an index called the TIOBE Index.
TIOBE index provides a measure for the popularity of programming languages as mined from search engines. It includes many browser results as well as many programming languages. The index is published every month and for the month of January you can find it here:
http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html

Programming languages C and Java are the top dogs and Javascript jumped from 9 to 7 in January 2015 and C# steady from 2014 to 2015 at 5.

TIOBE Index is calculated by the query +"Language> programming" to the search engines.

Get more info on TIOBE herre:
http://www.tiobe.com/index.php/content/products/tics/TICS_framework.html

Where do I find the C# Compiler on my computer?

The C# compiler CSC.exe is found here:
  C:\Windows\Microsoft.NET\Framework\v4.0.30319\Csc.exe

This is on a Windows 8.1 Professional machine.

In any case search in this folder by changing the directory as shown below
C:/ cd %Windir%/Microsoft.NET/Framework

You may find more than one Framework on your computer
The one shown in the beginning of this post is for version 4.0.30319

Can I work on Stored Procedures using LinqPad?

Of course you can. In LinqPad version 4.51.03 you can easily run stored procedures you have created using both SQL and C# Expression.

For example, after connecting to AdvventureWorks2012 database I can see all the stored procedures. Right clicking a stored procedure and choosing StoredProceedureName(...) drop-down, you display the stored procedure in the query window. You need to insert the parameters inside the parenthesis containing the ellipsis and run the query.

Examples are shown in the following two posts:

http://hodentekmsss.blogspot.com/2015/01/learn-querying-sql-server-2012-using.html

http://hodentekmsss.blogspot.com/2015/01/learn-querying-sql-server-2012-using_25.html