Dropping a Function if Exists in Database

IF EXISTS (
    SELECT * FROM sysobjects WHERE id = object_id(N'function_name') 
    AND xtype IN (N'FN', N'IF', N'TF')
)
    DROP FUNCTION function_name
GO

or

IF object_id(N'function_name', N'FN') IS NOT NULL
    DROP FUNCTION function_name
GO