In the previous code sample, notice that two constants were used in place of the database connection string and database path in the Microsoft® ActiveX® Data Object (ADO) Recordset object's Open method. This sample highlights another important consideration when you are writing reusable code: Avoid hard-coding values used in your code. If a string or number is used repeatedly, define a module-level constant and use the constant in your code. If you must use a string or number in more than one module, declare the constant by using the Public keyword. If you have a string or number that is local to a procedure, consider rewriting the procedure to pass the value as an argument or by using a local constant.
Try to minimize the number of arguments in a procedure and pass in only what is actually required by the procedure. In addition, make sure your procedures use all the arguments passed to them.
Group related procedures and the constants they use together in the same module, and where appropriate, consider grouping related procedures together in a class module with a clearly defined interface.
Keep procedures in standard modules and not in modules behind forms or documents. The code in form modules should be only that code that is tied directly to the form itself and the code required for calling general procedures stored in standard modules.
Communicate between procedures by passing data as arguments to the procedures. Persist data by writing it to disk or to the Windows registry. Avoid using a procedure to write to a global variable so another procedure can read data from that global variable. Avoid communicating with another procedure by passing data out of the application, for example, using one procedure to write data to a disk file, .ini file, or the registry so another procedure can read that data.
The same considerations that go into writing reusable code also apply to writing reusable script. The easiest way to reuse script is to group related procedures together in a scriptlet and then link the scriptlet to the HTML page in which you want to use the script.