JE::Object(3pm) User Contributed Perl Documentation JE::Object(3pm)
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
perl v5.14.2 2012-03-18 JE::Object(3pm)