Annotated ECMAScript 5.1
‟Ex igne vita”
‟Ex igne vita”
Instances of Error objects are thrown as exceptions when runtime errors occur. The Error objects may also serve as base objects for user-defined exception classes.
When
Error is
called as a function rather than as a constructor, it creates and
initialises a new Error object. Thus the function call Error(…)
is equivalent to the object creation expression new
Error(…)
with the same arguments.
The
[[Prototype]] internal property of the newly constructed object is
set to the original Error prototype object, the one that is the
initial value of Error.prototype
(15.11.3.1).
The
[[Class]] internal property of the newly constructed object is set
to "Error".
The [[Extensible]] internal property of the newly constructed object is set to true.
If
the argument message
is not undefined, the message
own property of the newly constructed object is set to
ToString(message).
When
Error is called as
part of a new
expression, it is a constructor: it initialises the newly created
object.
The
[[Prototype]] internal property of the newly constructed object is
set to the original Error prototype object, the one that is the
initial value of Error.prototype
(15.11.3.1).
The
[[Class]] internal property of the newly constructed Error object is
set to "Error".
The [[Extensible]] internal property of the newly constructed object is set to true.
If
the argument message
is not undefined, the message
own property of the newly constructed object is set to
ToString(message).
The value of the [[Prototype]] internal property of the Error constructor is the Function prototype object (15.3.4).
Besides
the internal properties and the length
property (whose value is 1), the Error constructor has the
following property:
The
initial value of Error.prototype
is the Error prototype object (15.11.4).
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
The
Error prototype object is itself an Error object (its [[Class]] is
"Error").
The value of the [[Prototype]] internal property of the Error prototype object is the standard built-in Object prototype object (15.2.4).
The
initial value of Error.prototype.constructor
is the built-in Error
constructor.
The
initial value of Error.prototype.name
is "Error".
The
initial value of Error.prototype.message
is the empty String.
The following steps are taken:
Let O be the this value.
Let
name be the result of calling the [[Get]] internal method of
O with argument "name".
If
name is undefined, then let name be "Error";
else let name be ToString(name).
Let
msg be the result of calling the [[Get]] internal method of
O with argument "message".
If msg is undefined, then let msg be the empty String; else let msg be ToString(msg).
If name and msg are both the empty String, return "Error".
If name is the empty String, return msg.
If msg is the empty String, return name.
Return the result of concatenating name, ":", a single space
character, and msg.
Error
instances inherit properties from the Error prototype object and
their [[Class]] internal property value is "Error".
Error instances have no special properties.
One of the NativeError objects below is thrown when a runtime error is detected. All of these objects share the same structure, as described in 15.11.7.
This exception is not currently used within this specification. This object remains for compatibility with previous editions of this specification.
Indicates a numeric value has exceeded the allowable range. See 15.4.2.2, 15.4.5.1, 15.7.4.2, 15.7.4.5, 15.7.4.6, and 15.7.4.7, 15.9.5.43.
Indicate that an invalid reference value has been detected. See 8.7.1, 8.7.2, 10.2.1, 10.2.1.1.4, 10.2.1.2.4, and 11.13.1.
Indicates that a parsing error has occurred. See 11.1.5, 11.3.1, 11.3.2, 11.4.1, 11.4.4, 11.4.5, 11.13.1, 11.13.2, 12.2.1, 12.10.1, 12.14.1, 13.1, 15.1.2.1, 15.3.2.1, 15.10.2.2, 15.10.2.5, 15.10.2.9, 15.10.2.15, 15.10.2.19, 15.10.4.1, and 15.12.2.
Indicates the actual type of an operand is different than the expected type. See 8.6.2, 8.7.2, 8.10.5, 8.12.5, 8.12.7, 8.12.8, 8.12.9, 9.9, 9.10, 10.2.1, 10.2.1.1.3, 10.6, 11.2.2, 11.2.3, 11.4.1, 11.8.6, 11.8.7, 11.3.1, 13.2, 13.2.3, 15, 15.2.3.2, 15.2.3.3, 15.2.3.4, 15.2.3.5, 15.2.3.6, 15.2.3.7, 15.2.3.8, 15.2.3.9, 15.2.3.10, 15.2.3.11, 15.2.3.12, 15.2.3.13, 15.2.3.14, 15.2.4.3, 15.3.4.2, 15.3.4.3, 15.3.4.4, 15.3.4.5, 15.3.4.5.2, 15.3.4.5.3, 15.3.5, 15.3.5.3, 15.3.5.4, 15.4.4.3, 15.4.4.11, 15.4.4.16, 15.4.4.17, 15.4.4.18, 15.4.4.19, 15.4.4.20, 15.4.4.21, 15.4.4.22, 15.4.5.1, 15.5.4.2, 15.5.4.3, 15.6.4.2, 15.6.4.3, 15.7.4, 15.7.4.2, 15.7.4.4, 15.7.4.8 [?], 15.9.5, 15.9.5.44, 15.10.4.1, 15.10.6, 15.11.4.4 and 15.12.3.
Indicates that one of the global URI handling functions was used in a way that is incompatible with its definition. See 15.1.3.
When
an ECMAScript implementation detects a runtime error, it throws an
instance of one of the NativeError objects defined in
15.11.6. Each of these objects has the structure described below,
differing only in the name used as the constructor name instead of
NativeError, in the name property of the prototype
object, and in the implementation-defined message
property of the prototype object.
For each error object, references to NativeError in the definition should be replaced with the appropriate error object name from 15.11.6.
When a NativeError constructor is called as a function rather than as a constructor, it creates and initialises a new object. A call of the object as a function is equivalent to calling it as a constructor with the same arguments.
The
[[Prototype]] internal property of the newly constructed object is
set to the prototype object for this error constructor. The
[[Class]] internal property of the newly constructed object is set
to "Error".
The [[Extensible]] internal property of the newly constructed object
is set to true.
If
the argument message
is not undefined, the message
own property of the newly constructed object is set to
ToString(message).
When
a NativeError constructor is called as part of a new
expression, it is a constructor: it initialises the newly created
object.
The
[[Prototype]] internal property of the newly constructed object is
set to the prototype object for this NativeError constructor.
The [[Class]] internal property of the newly constructed object is
set to "Error".
The [[Extensible]] internal property of the newly constructed object
is set to true.
If
the argument message
is not undefined, the message
property of the newly constructed object is set to
ToString(message).
The value of the [[Prototype]] internal property of a NativeError constructor is the Function prototype object (15.3.4).
Besides
the internal properties and the length
property (whose value is 1), each NativeError
constructor has the following property:
The
initial value of NativeError.prototype
is a NativeError prototype object (15.11.7.7). Each
NativeError constructor has a separate prototype object.
This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.
Each
NativeError prototype object is an Error object (its
[[Class]] is "Error").
The value of the [[Prototype]] internal property of each NativeError prototype object is the standard built-in Error prototype object (15.11.4).
The
initial value of the constructor
property of the prototype for a given NativeError constructor
is the NativeError constructor function itself (15.11.7).
The
initial value of the name
property of the prototype for a given NativeError constructor
is the name of the constructor (the name used instead of
NativeError).
The
initial value of the message
property of the prototype for a given NativeError constructor
is the empty String.
NOTE The
prototypes for the NativeError constructors do not themselves
provide a toString function,
but instances of errors will inherit it from the Error prototype
object.
NativeError
instances inherit properties from their NativeError prototype
object and their [[Class]] internal property value is "Error".
NativeError instances have no special properties.