JE::Object - Base class for all JavaScript objects


  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;

  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.


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.


$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:


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.


This returns the string 'object'.


Returns the string 'Object'.


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.


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.


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
  $$self->{keys}           an array of the names of enumerable
  $$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.