Signals the occurrence of an error. This signal can be caught by a try-catch statement.

Throw Expression



A value to store in catch's OutputVar.

Since this parameter is an expression, all of the following are valid examples:

throw 3
throw "literal string"
throw MyVar
throw i + 1
throw { what: "Custom error", file: A_LineFile, line: A_LineNumber } ; Throws an object

This parameter is always an expression, so variable references should not be enclosed in percent signs except to perform a dereferencing.

If omitted, an exception object is thrown with a default message.

Exception(Message [, What, Extra])

Creates an object with the following properties, also common to exceptions created by runtime errors:

If What is omitted, it defaults to the name of the current function or subroutine. Otherwise it can be a string or a negative offset from the top of the call stack. For example, a value of -1 sets Exception.What to the current function or subroutine and Exception.Line to the line which called it. However, if the script is compiled or the offset is invalid, What is simply converted to a string.

Message and Extra are converted to strings. These are displayed by an error dialog if the exception is thrown and not caught.

catch e
    MsgBox("Error in " e.What ", which was called at line " e.Line)

SomeFunction() {
    throw Exception("Fail", -1)


Try, Catch, Finally


See Try.