Annotated ECMAScript 5.1
‟Ex igne vita”
‟Ex igne vita”
There are certain built-in objects available whenever an ECMAScript program begins execution. One, the global object, is part of the lexical environment of the executing program. Others are accessible as initial properties of the global object.
Unless
specified otherwise, the [[Class]] internal property of a built-in
object is "Function"
if that built-in object has a [[Call]] internal property, or
"Object"
if that built-in object does not have a [[Call]] internal property.
Unless specified otherwise, the [[Extensible]] internal property of
a built-in object initially has the value true.
Many
built-in objects are functions: they can be invoked with arguments.
Some of them furthermore are constructors: they are functions
intended for use with the new
operator. For each built-in function, this specification describes
the arguments required by that function and properties of the
Function object. For each built-in constructor, this specification
furthermore describes properties of the prototype object of that
constructor and properties of specific object instances returned by
a new expression
that invokes that constructor.
Unless otherwise specified in the description of a particular function, if a function or constructor described in this clause is given fewer arguments than the function is specified to require, the function or constructor shall behave exactly as if it had been given sufficient additional arguments, each such argument being the undefined value.
Unless otherwise specified in the description of a particular function, if a function or constructor described in this clause is given more arguments than the function is specified to allow, the extra arguments are evaluated by the call and then ignored by the function. However, an implementation may define implementation specific behaviour relating to such arguments as long as the behaviour is not the throwing of a TypeError exception that is predicated simply on the presence of an extra argument.
NOTE Implementations that add additional capabilities to the set of built-in functions are encouraged to do so by adding new functions rather than adding new parameters to existing functions.
Every
built-in function and every built-in constructor has the
Function prototype object, which is the initial value of the expression
Function.prototype
(15.3.4), as the value of its [[Prototype]] internal property.
Unless
otherwise specified every built-in prototype object has the
Object prototype object, which is the initial value of the expression
Object.prototype
(15.2.4), as the value of its [[Prototype]] internal property,
except the Object prototype object itself.
None
of the built-in functions described in this clause that are not
constructors shall implement the [[Construct]] internal method
unless otherwise specified in the description of a particular
function. None of the built-in functions described in this clause
shall have a prototype
property unless otherwise specified in the description of a
particular function.
This clause generally describes distinct behaviours for when a constructor is “called as a function” and for when it is “called as part of a new expression”. The “called as a function” behaviour corresponds to the invocation of the constructor’s [[Call]] internal method and the “called as part of a new expression” behaviour corresponds to the invocation of the constructor’s [[Construct]] internal method.
Every
built-in Function object described in this clause—whether as a
constructor, an ordinary function, or both—has a length
property whose value is an integer. Unless otherwise specified, this
value is equal to the largest number of named arguments shown in the
subclause headings for the function description, including optional
parameters.
NOTE For
example, the Function object that is the initial value of the slice
property of the String prototype object is described under the
subclause heading “String.prototype.slice (start, end)” which
shows the two named arguments start and end; therefore the value of
the length property of
that Function object is 2.
In
every case, the length
property of a built-in Function object described in this clause has
the attributes { [[Writable]]: false, [[Enumerable]]:
false, [[Configurable]]: false }. Every other property
described in this clause has the attributes { [[Writable]]: true,
[[Enumerable]]: false, [[Configurable]]: true } unless
otherwise specified.