=head1 NAME
JE::Types - JavaScript types and objects
This is just documentation, not a module.
=head1 DESCRIPTION
The various JavaScript types and objects are represented by Perl
classes in JE (which are listed below). This document describes the basic
interface implemented by
these classes. Information specific to each class can be found on its own
manual page.
=head1 UPGRADING VALUES
When a value is passed from Perl to JavaScript, it will be "upgraded" to a
Perl object
representing a JavaScript value. This is done by the C<upgrade> method of
the global object.
If the value to be upgraded is a blessed reference, and the class into
which it is blessed has been bound using JE's C<bind_class> method, it is
wrapped up in a proxy object that provides the methods JS needs. A blessed
reference whose class has not been bound will be
left alone (we assume you know what you are doing).
Otherwise the
conversion is as follows:
From To
-------------------------
undef undefined
array ref Array
hash ref Object
code ref Function
'0' number
other scalar string
B<WARNING:> The 'upgrading' of simple scalars (strings/numbers) and regexps
is still
subject to change.
B<To do:> Make &JE::upgrade detect whether a simple scalar is a string or
number.
B<To do:> Convert Regexp objects to
JE::Object::RegExp objects.
=head1 WHICH CLASSES ARE WHICH
Each built-in JavaScript class or primitive type is a Perl class
underneath. Here
is the complete list of object classes:
JavaScript Perl
-----------------
Object JE::Object
Function JE::Object::Function
Array JE::Object::Array
String JE::Object::String
Boolean JE::Object::Boolean
Number JE::Object::Number
Date JE::Object::Date
RegExp JE::Object::RegExp
Error JE::Object::Error
RangeError JE::Object::Error::RangeError
ReferenceError JE::Object::Error::ReferenceError
SyntaxError JE::Object::Error::SyntaxError
TypeError JE::Object::Error::TypeError
URIError JE::Object::Error::URIError
And here are the primitive types:
string JE::String
number JE::Number
boolean JE::Boolean
null JE::Null
undefined JE::Undefined
And I might also mention a few special cases:
Global JE
Math JE::Object::Math
Arguments JE::Object::Function::Arguments
Function scope JE::Object::Function::Call
RegExp constructor JE::Object::Function::RegExpConstructor
The last three are for internal use.
=head1 PUBLIC API
=head2 Using JS Values as Scalars
Every JS data type can be used as a string, boolean or number. It works
exactly as it does in JavaScript. For example:
$num = $je->eval('42');
$num2 = $je->eval('NaN');
print $num2; # prints NaN
print 0+$num2; # prints nan or NaN, depending or your system
# (or something really weird on Windows).
$zero_str = $je->eval("'0'");
print "true" if $zero_str; # prints 'true'
print "false" unless 0+$zero_str; # prints 'false'
$false = $je->eval('false');
print $false; # prints 'false'
print "false" unless $false; # also prints 'false'
=head2 Property Access
To access the property of a JS object,
or of the
JS environment itself (i.e., a global variable), just use it as a hash ref:
$je->{String}; # gives you the String constructor function
$je->{undefined}; # the undefined value
my $obj = $je->eval('var obj = new Object; return obj');
$obj->{foo} = 'bar';
C<keys> will return a list of the object's enumerable properties, including
those inherited from its prototype. The following example prints
S<'baz foo '>:
$obj = $je->eval('Object.prototype.foo="bar"; ({baz:43}) ');
print "$_ " for keys %$obj;
C<exists> and C<delete> act upon properties of the object itself, ignoring
those of
its prototype, so C<< exists $obj->{foo} >> will return false.
=head2 Calling Methods
To call a method on an object or primitive data type, use the C<method>
method:
my $number = $je->eval('42');
$number->method('toString', 16); # returns the number in hexadecimal
=head2 Calling Functions
Just use a function as though it were a coderef:
$je->{Array}->();
If you need to specify the invocant ('this' value), use the C<call_with>
method:
$je->{Number}{prototype}{toString}->call_with($je->eval('42'), 16);
=head2 Just Getting a Simple Perl Scalar
To convert one of the fancy objects returned by JE into a simple Perl
value, use the C<value> method.
$number->value; # simple Perl scalar
$str->value; # likewise
$obj->value; # hash ref
$array->value; # array ref
Currently the C<value> method of objects and arrays is not recursive, but
I plan to make it so later on. The only way to get consistent behaviour
between this and future versions is to pass C<< recursive => 0 >> as
arguments.
=head1 DATA TYPE API (in more detail)
If you are going to write your own custom data types, proxy objects, or
subclasses of JE's classes, you'll need to read
this. If not, you shouldn't need to, but you might like to anyway. :-)
Be warned that some of the methods described here can be hard
to use, and can easily result in code that's hard to debug, if misused.
This applies to those that expect their arguments already to be objects
compatible with the JE::Types interface. If you are not sure that a value you have is such, run it through the global object's C<upgrade> method (or
just use the L</PUBLIC API>, above).
These are the methods that the JavaScript engine itself uses (as opposed
to those provided for convenient access from the Perl side). Each class
provides whichever of the following methods are applicable. If
an object does not support a particular method, a TypeError will be thrown
when JavaScript code (indirectly) tries to call that method. (For
instance,
C<'some_string'()> will attempt to call the C<call> method of JE::String,
thus resulting in a TypeError).
=over 4
=item prop($name)
=item prop($name, $new_value)
Gets or sets a property. Setting a property returns the new
value. The return value will be a Perl undef if the
property does not exist. See also L<JE::Object>, for the
S<< C<prop({ ... })> >> usage.
The new value is expected already to be an object compatible with the
JE::Types interface.
=item keys
Returns a list of the names of enumerable properties. This is a list of
Perl strings, not JE::Strings.
=item delete($name)
Deletes the property named $name, if it is deletable. If the property did
not exist or it was deletable, then
true is returned. If the property exists and could not be deleted, false
is returned.
L<JE::Object> will also take a second argument, that allows one to
indicate whether an undeletable property should be deleted. This is
required by custom classes if the object in question is the global object.
The return value is a Perl scalar, not a JE::Boolean.
=item value
This returns a value that is supposed to be useful in Perl. The
C<< value >> method of a JE::Object::Array,
for instance, produces an array ref.
=item call(@args)
Runs the code associated with the object if it is a function.
The arguments are passed as-is, and are not upgraded.
=item apply($obj, @args)
Runs the code associated with the object if it is a function. C<$obj> will
be passed to the function as its invocant (its 'this' value).
The arguments are passed, as-is, and are not upgraded.
=item construct(@args)
This is just like calling a function
in JS with the C<new> keyword (which itself calls this method). It calls
the constructor, if this
function has one (functions written in JS
don't have this). Otherwise, an empty object will be created and passed to
the
function as its invocant. The return value of the function will be
returned if it is an object. Otherwise it will be discarded, and the
object
originally passed to the function will be returned instead (possibly
modified).
=begin comment
NOTE: I need to copy parts of this to those classes that don't describe the
C<new> method, before I go and delete it.
=item I<Class>->new($global_obj, @args)
The C<@args> are in the same order that they are passed to the constructor
function in JavaScript (for objects, not primitives. For primitive
classes,
there should be only two
arguments, the global object and the value).
Some object classes also provide a hash ref syntax. See each object
class's
respective man page.
User-defined classes do not need to accept arguments in the same order as
those that come with JE. They can do whatever they like.
=end comment
=item exists($property_name)
Returns a boolean indicating whether the property exists and is not
inherited from a prototype. Used by
C<Object.prototype.hasOwnProperty>. (The C<in> operator checks to see
whether
the return value of C<prop> is defined.)
B<To do:> Implement this method in subclasses of JE::Object.
=item is_readonly($property_name)
Not supported by the primitive JE classes. This returns a boolean
indicating whether a given property is readonly. If
it doesn't exist, then the C<is_readonly> method of the object's prototype
is called with the same arguments. If there is no prototype, false is
returned.
This is used internally by JE::Object's C<prop> method.
=item is_enum($property_name)
Not supported (yet) by the primitive JE classes. This returns a boolean
indicating whether a given property is enumerable.
This is used by C<Object.prototype.propertyIsEnumerable>.
=item typeof
Returns a Perl string containing the type of the object. Used
by the JS C<typeof> operator.
=item class
This applies to object classes only (though it is going to change, so that
primitives can pretend to be objects). It returns
a
Perl string containing
the type of object. This is only used by the default JavaScript
C<toString> method. If you create your own object class without
subclassing JE::Object,
you should I<still> provide the C<class> method, so that this
JS code will still work:
YourClass.prototype.toString = Object.prototype.toString;
(new YourClass).toString();
=item id
This returns a unique id for the object or primitive, used by
the JavaScript C<===>
operator. This id is unique as a I<string,> not as a number.
The JE primitive classes provide a unique string beginning with the data
type. The JE::Object and its subclasses return the memory address of the
object itself. If you
subclass JE::Object, you should not have to
implement this method, unless you have multiple objects that you would
like JS to consider the same object.
Note that the id 'num:nan' is treated specially. It is never
considered equal to itself.
=item primitive
Returns true or false.
=item prototype
=item prototype ( $obj )
This applies to objects only, not to primitives. This method returns the
prototype of the object, or undef if there is no prototype. If C<$obj> is
specified,
the prototype is set to that object first. The C<prop> method uses this
method, as does C<< JE::Object->new >>.
=item to_primitive($preferred_type)
=item to_boolean
=item to_string
=item to_number
=item to_object
These each perform the appropriate type conversion. $preferred_type, which
is
optional, must be either 'string' or 'number'.
Calling C<to_string> or C<to_number> on a object is not exactly the same as
calling
C<to_primitive('string')> or C<to_primitive('number')>, because the
argument to C<to_primitive> is merely a I<suggestion.>
The last four methods in this list should not be overridden by subclasses
of JE::Object.
=item global
Returns a reference to the global object.
=item taint($taint_brush)
This will only be called if it is implemented. Of JE's types, only
primitive strings and numbers implement this.
C<$taint_brush> will always be a tainted empty string. If the
object's internal value is not tainted, this method should return a tainted
clone
of
the object. Otherwise, it should return the object itself.
=back
=head1 SEE ALSO
L<JE> and all the modules listed above under L</WHICH CLASSES ARE WHICH>.
=cut