Error Object (JavaScript)

errorObj

Required. The variable name to which the Error object is assigned. The variable assignment is omitted when you create the error using a throw statement.

number

Optional. Numeric value assigned to an error. Zero if omitted.

description

Optional. Brief string that describes an error. Empty string if omitted.

Whenever a run-time error occurs, an instance of the Error object is created to describe the error. This instance has two intrinsic properties that contain the description of the error (description property) and the error number (number property).

An error number is a 32-bit value. The upper 16-bit word is the facility code, while the lower word is the actual error code.

Error objects can also be explicitly created, using the syntax shown above, or thrown using the throw statement. In both cases, you can add any properties you choose to expand the capability of the Error object.

Typically, the local variable that is created in a try...catch statement refers to the implicitly created Error object. As a result, you can use the error number and description in any way you choose.

The following example illustrates the use of the Error object.

function checkInput(x) {
    try
    {
        if (isNaN(parseInt(x))) {
            throw new Error("Input is not a number.");
        }
    }
    catch(e)
    {
        document.write(e.description);
    }
}

The following example illustrates the use of the implicitly created Error object.

try
   {
   // Cause an error.
   x = y;
   }
catch(e)
   {
      document.write(e);
      document.write ("<br />");

      document.write ("Number: ");
      document.write (e.number & 0xFFFF);
      document.write ("<br />");

      document.write ("Facility Code: ");
      document.write(e.number>>16 & 0x1FFF);
      document.write ("<br />");

      document.write ("Description: ");
      document.write (e.description);
   }

// Output:
// ReferenceError: 'y' is undefined
// Number: 5009
// Facility Code: 10
// Description: 'y' is undefined

toString Method (Error) | valueOf Method (Date)

constructor Property (Error) | description Property | message Property | name Property | number Property | prototype Property (Error) | stack Property (Error) (JavaScript) | stackTraceLimit Property (Error) (JavaScript)

Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards, Internet Explorer 10 standards. Also supported in Windows Store apps. See Version Information.

Reference