How to view a stored function - SQL Server

select definition 
from sys.sql_modules 
where object_name(object_id) like 'functionName'

You can use sp_helptext command to view the definition. It simply does

Displays the definition of a user-defined rule, default, unencrypted Transact-SQL stored procedure, user-defined Transact-SQL function, trigger, computed column, CHECK constraint, view, or system object such as a system stored procedure.

E.g;

EXEC sp_helptext 'StoredProcedureName'

EDIT: If your databases or server are different then you can do it by specifying them as well

EXEC [ServerName].[DatabaseName].dbo.sp_helptext 'storedProcedureName'

--ShowStoredProcedures
select p.[type]
      ,p.[name]
      ,c.[definition]
  from sys.objects p
  join sys.sql_modules c
    on p.object_id = c.object_id
 where p.[type] = 'P'
   --and c.[definition] like '%foo%'
ORDER BY p.[name]
___________

SELECT OBJECT_NAME(object_id) ProcedureName,
       definition
FROM sys.sql_modules
WHERE objectproperty(object_id,'IsProcedure') = 1
ORDER BY OBJECT_NAME(object_id)