Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Availability

JavaScript
1.5; JScript 5.5; ECMAScript v3

Inherits from/Overrides

Inherits from Object

Constructor

new Error( )
new Error(message)

Arguments

message

An optional error message that provides details about the exception.

Returns

A newly constructed Error object. If the
message argument is specified, the Error
object will use it as the value of its message
property; otherwise, it will use an implementation-defined default
string as the value of that property. When the Error(
) constructor is called as a function, without the
new operator, it behaves just as it does when
called with the new operator.

Properties

message

An error message that provides details about the exception. This
property holds the string passed to the constructor or an
implementation-defined default string.

name

A string that specifies the type of the exception. For instances of
the Error class and all of its subclasses, this property specifies
the name of the constructor used to create the instance.

Methods

toString( )

Returns an implementation-defined string that represents this Error
object.

Description

Instances of the Error class
represent errors or exceptions and are typically used with the
throw and try/catch statements.
The name property specifies the type of the
exception, and the message property can be used to
provide human-readable details about the exception.

The JavaScript interpreter never throws Error object directly;
instead, it throws instances of one of the Error subclasses such as
SyntaxError or RangeError. In your own code you may find it
convenient to throw Error objects to signal exceptions, or you may
prefer to simply throw an error message or error code as a primitive
string or number value.

Note that the ECMAScript specification defines a toString(
) method for the Error class (it is inherited by each of
the subclasses of Error) but that it does not require this
toString( ) method to return a string that
contains the contents of the message property.
Therefore, you should not expect the toString( )
method to convert an Error object to convert to a meaningful
human-readable string. To display an error message to a user, you
should explicitly use the name and
message properties of the Error object.

Example

You might signal an exception with code like the following:

function factorial(x) {
if (x < 0) throw new Error("factorial: x must be >= 0");
if (x <= 1) return 1; else return x * factorial(x-1);
}

And if you catch an exception, you might display its to the user with
code like the following (which uses the client-side
Window.alert( ) method):

try { &*(&/* an error is thrown here */ }
catch(e) {
if (e instanceof Error) {  // Is it an instance of Error or a subclass?
alert(e.name + ": " + e.message);
}
} 

See Also

EvalError, RangeError, ReferenceError, SyntaxError, TypeError,
URIError