try...catch...finally Statement (Windows Scripting - JScript)

 

Implements error handling for JScript.

Syntax

try {
   tryStatements}catch(exception){
   catchStatements}finally {finallyStatements}

Arguments

• tryStatements
  Required. Statements where an error can occur.

• exception
  Required. Any variable name. The initial value of exception is the value of the thrown error.

• catchStatements
  Optional. Statements to handle errors occurring in the associated tryStatements.

• finallyStatements
  Optional. Statements that are unconditionally executed after all other error processing has occurred.

Remarks

The try...catch...finally statement provides a way to handle some or all of the possible errors that may occur in a given block of code, while still running code. If errors occur that the programmer has not handled, JScript simply provides its normal error message to a user, as if there was no error handling.

The tryStatements contain code where an error can occur, while catchStatements contain the code to handle any error that does occur. If an error occurs in the tryStatements, program control is passed to catchStatements for processing. The initial value of exception is the value of the error that occurred in tryStatements. If no error occurs, catchStatements are never executed.

If the error cannot be handled in the catchStatements associated with the tryStatements where the error occurred, use the throw statement to propagate, or rethrow, the error to a higher-level error handler.

After all statements in tryStatements have been executed and any error handling has occurred in catchStatements, the statements in finallyStatements are unconditionally executed.

Notice that the code inside finallyStatements is executed even if a return statement occurs inside the try or catch blocks, or if the catch block re-throws the error. finallyStatements are guaranteed to always run, unless an unhandled error occurs (for example, causing a run-time error inside the catch block).

Legacy Code Example

The following example causes a TypeError exception to be thrown and displays the name of the error and its message.

try
{
    // Cause an error.
    var x = y;
}
catch(e)
{
    document.write ("Error Message: " + e.message);
    document.write ("<br />");
    document.write ("Error Code: ");
    document.write (e.number & 0xFFFF)
    document.write ("<br />");
    document.write ("Error Name: " + e.name);
}

Legacy Code Example

The following example shows how JScript exception handling works.

try
    {
    ShowLine("Outer try running..");
 
    try
        {
        ShowLine("Nested try running...");
        throw new Error(301, "an error");
        }
    catch(e)
        {
        ShowLine("Nested catch caught " + e.message);
        throw e;
        }
    finally
        {
        ShowLine("Nested finally is running...");
        }   
    }
catch(e)
    {
    ShowLine("Outer catch caught " + e.message);
    }
finally
    {
    ShowLine("Outer finally running");
    }


function ShowLine(s)
    {
    document.write(s);
    document.write ("<br />");
    }

This produces the following output:

Outer try running..
Nested try running...
Nested catch caught an error
Nested finally is running...
Outer catch caught an error
Outer finally running

Requirements

Version 5

Change History

Date	History	Reason
September 2009	Modified second example.	Information enhancement.
April 2009	Added another example.	Customer feedback.
March 2009	Reformatted example.	Information enhancement.

See Also

throw Statement (Windows Scripting - JScript)