Not Handling Errors

You should always check for unexpected user input, such as a string when prompted for a number, or a number value outside the bounds of what the program can use. Likewise, you must anticipate errors from within the program, and understand the meaning of values returned by the functions you use.

To handle internal program errors in VBScript, you must use the On Error Resume Next statement. Without this instruction, the script will abort as soon as the error is detected, which prevents you from quietly handling errors with script. Here are a few precautions to keep in mind when using the On Error Resume Next statement:

• When debugging it is often necessary to disable error handling so that you can determine where errors are occurring. Reenable it when you are finished debugging.
• Because you are resuming program execution at the next statement whenever an error occurs, you should avoid using script that might produce an error as the logic portion of an If statement, or the test of a While loop. If these statements cause errors, the inner logic of the If statement will be executed, and the While loop will never complete.