Throw

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

Throw Value

Parameters

Value

A value to throw; typically an Error object. For example:

throw ValueError("Parameter #1 invalid", -1, theBadParam)

Values of all kinds can be thrown, but if Catch is used without specifying a class (or Try is used without Catch or Finally), it will only catch instances of the Error class.

While execution is within a Catch, Value can be omitted to re-throw the caught value (avoiding the need to specify an output variable just for that purpose). This is supported even within a nested Try-Finally, but not within a nested Try-Catch. The line with throw does not need to be physically contained by the Catch statement's body; it can be used by a called function.

Remarks

The space or tab after throw is optional if the expression is enclosed in parentheses, as in throw(Error()).

A thrown value or runtime error can be caught by Try-Catch. In such cases, execution is transferred into the catch statement or to the next statement after the try. If a thrown value is not caught, the following occurs:

• Any active OnError callbacks are called. Each callback may inspect Value and either suppress or allow further callbacks and default handling.
• By default, an error message is displayed based on what was thrown. If Value is an Object and owns a value property named Message, its value is used as the message. If Value is a non-numeric string, it is used as the message. In any other case, a default message is used. If Value is numeric, it is shown below the default message.
• The thread exits. Note that this does not necessarily occur for continuable errors, but throw is never continuable.

Related

Error Object, Try, Catch, Finally, OnError

Examples

See Try.