NAME¶
JE::Object - Base class for all JavaScript objects
SYNOPSIS¶
use JE;
use JE::Object;
$j = new JE;
$obj = new JE::Object $j;
$obj->prop('property1', $new_value); # sets the property
$obj->prop('property1'); # returns $new_value;
$obj->{property1} = $new_value; # or use it as a hash
$obj->{property1}; # ref like this
$obj->keys; # returns a list of the names of enumerable property
keys %$obj;
$obj->delete('property_name');
delete $obj->{property_name};
$obj->method('method_name', 'arg1', 'arg2');
# calls a method with the given arguments
$obj->value ; # returns a value useful in Perl (a hashref)
"$obj"; # "[object Object]" -- same as $obj->to_string->value
0+$obj"; # nan -- same as $obj->to_number->value
# etc.
DESCRIPTION¶
This module implements JavaScript objects for JE. It serves as a base class for
all other JavaScript objects.
A JavaScript object is an associative array, the elements of which are its
properties. A method is a property that happens to be an instance of the
"Function" class ("JE::Object::Function").
JE::Object objects can be used in Perl as a number, string or boolean. The
result will be the same as in JavaScript. The "%{}" (hashref)
operator is also overloaded and returns a hash that can be used to modify the
object. See "USING AN OBJECT AS A HASH".
See also JE::Types for descriptions of most of the methods. Only what is
specific to JE::Object is explained here.
METHODS¶
- $obj = JE::Object->new( $global_obj )
- $obj = JE::Object->new( $global_obj, $value )
- $obj = JE::Object->new( $global_obj, \%options )
- This class method constructs and returns a new JavaScript
object, unless $value is already a JS object, in which case it just
returns it. The behaviour is the same as the "Object"
constructor in JavaScript.
The %options are as follows:
prototype the object to be used as the prototype for this
object (Object.prototype is the default)
value the value to be turned into an object
"prototype" only applies when "value" is omitted, undef,
undefined or null.
To convert a hash into an object, you can use the hash ref syntax like this:
new JE::Object $j, { value => \%hash }
Though it may be easier to write:
$j->upgrade(\%hash)
The former is what "upgrade" itself uses.
- $obj->new_function($name, sub { ... })
- $obj->new_function(sub { ... })
- This creates and returns a new function object. If $name is
given, it will become a property of the object. The function is
enumerable, like "alert" et al. in web browsers.
For more ways to create functions, see JE::Object::Function.
- $obj->new_method($name, sub { ... })
- $obj->new_method(sub { ... })
- This is the same as "new_function", except that
the subroutine's first argument will be the object with which the function
is called, and that the property created will not be enumerable. This
allows one to add methods to "Object.prototype", for instance,
without making every for-in loop list that method.
For more ways to create functions, see JE::Object::Function.
- $obj->prop( $name )
- $obj->prop( $name => $value )
- $obj->prop({ ... })
- See "JE::Types" for the first two uses.
When the "prop" method is called with a hash ref as its argument,
the prototype chain is not searched. The elements of the hash are
as follows:
name property name
value new value
dontenum whether this property is unenumerable
dontdel whether this property is undeletable
readonly whether this property is read-only
fetch subroutine called when the property is fetched
store subroutine called when the property is set
autoload see below
If "dontenum", "dontdel" or "readonly" is
given, the attribute in question will be set. If "value" is
given, the value of the property will be set, regardless of the
attributes.
"fetch" and "store", if specified, must be subroutines
for fetching/setting the value of the property. The 'fetch' subroutine
will be called with ($object, $storage_space) as the arguments, where
$storage_space is a hash key inside the object that the two subroutines
can use for storing the value (they can ignore it if they like). The
'store' subroutine will be call with ($object, $new_value, $storage_space)
as the arguments. Values assigned to the storage space from within these
routines are not upgraded, neither is the return value of
"fetch". "fetch" and "store" do not
necessarily have to go together. If you only specify "fetch",
then the value will be set as usual, but "fetch" will be able to
mangle the value when it is retrieved. Likewise, if you only specify
"store", the value will be retrieved the usual way, so you can
use this for validating or normalising the assigned value, for instance.
Note: Currently, a simple scalar or unblessed coderef in the
storage space will cause autoloading, but that is subject to change.
"autoload" can be a string or a coderef. It will be called/evalled
the first time the property is accessed (accessing it with a hash ref as
described here does not count). If it is a string, it will be evaluated in
the calling package (see warning below), in a scope that has a variable
named $global that refers to the global object. The result will become the
property's value. The value returned is not currently upgraded. The
behaviour when a simple scalar or unblessed reference is returned is
undefined. "autoload" will be ignored completely if
"value" or "fetch" is also given. Warning: The
'calling package' may not be what you think it is if a subclass overrides
"prop". It may be the subclass in such cases. To be on the safe
side, always begin the string of code with an explicit "package"
statement. (If anyone knows of a clean solution to this, please let the
author know.)
This hash ref calling convention does not work on Array objects when the
property name is "length" or an array index (a non-negative
integer below 4294967295). It does not work on String objects if the
property name is "length".
- $obj->delete($property_name,
$even_if_it's_undeletable)
- 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.
If the second argument is given and is true, the property will be deleted
even if it is marked is undeletable. A subclass may override this,
however. For instance, Array and String objects always have a 'length'
property which cannot be deleted.
- $obj->typeof
- This returns the string 'object'.
- $obj->class
- Returns the string 'Object'.
- $obj->value
- This returns a hash ref of the object's enumerable
properties. This is a copy of the object's properties. Modifying it does
not modify the object itself.
USING AN OBJECT AS A HASH¶
Note first of all that "\%$obj" is
not the same as
"$obj->value". The "value" method creates a new hash
containing just the enumerable properties of the object and its prototypes.
It's just a plain hash--no ties, no magic. %$obj, on the other hand, is
another creature...
%$obj returns a magic hash which only lists enumerable properties when you write
"keys %$obj", but still provides access to the rest.
Using "exists" on this hash will check to see whether it is the
object's
own property, and not a prototype's.
Assignment to the hash itself currently throws an error:
%$obj = (); # no good!
This is simply because I have not yet figured out what it should do. If anyone
has any ideas, please let me know.
Autovivification works, so you can write
$obj->{a}{b} = 3;
and the 'a' element will be created if did not already exist. Note that, if the
property "did" exist but was undefined (from JS's point of view),
this throws an error.
INNARDS¶
Each "JE::Object" instance is a blessed reference to a hash ref. The
contents of the hash are as follows:
$$self->{global} a reference to the global object
$$self->{props} a hash ref of properties, the values being
JavaScript objects
$$self->{prop_readonly} a hash ref with property names for the keys
and booleans (that indicate whether prop-
erties are read-only) for the values
$$self->{prop_dontdel} a hash ref in the same format as
prop_readonly that indicates whether proper-
ties are undeletable
$$self->{keys} an array of the names of enumerable
properties
$$self->{prototype} a reference to this object's prototype
In derived classes, if you need to store extra information, begin the hash keys
with an underscore or use at least one capital letter in each key. Such keys
will never be used by the classes that come with the JE distribution.
SEE ALSO¶
JE
JE::Types
