On Error - statement of language VBScript

Enables error-handling.
On Error Resume Next

If you don't use an On Error Resume Next statement, any runtime error that occurs is fatal; that is, an error message is displayed and the execution stops.

On Error Resume Next causes execution to continue with the statement immediately following the statement that caused the runtime error, or with the statement immediately following the most recent call out of the procedure containing the On Error Resume Next statement. This allows execution to continue despite a runtime error. You can then build the error-handling routine inline within the procedure. An On Error Resume Next statement becomes inactive when another procedure is called, so you should execute an On Error Resume Next statement in each called routine if you want inline error handling within that routine.

For similar purpose in the JavaScript language is used the command try...catch.
See also:
On Error Resume Next
Dim a, b
a = 0
b = 1/a 'Division by zero !!
If Err.Number>0 Then
  MsgBox ("Error " & Err.Number & " description=" & Err.Description)
End If
© MICROSYS, spol. s r. o.Tavičská 845/21 703 00 Ostrava-Vítkovice