NAME

JE::Types - JavaScript types and objects

This is just documentation, not a module.

DESCRIPTION

The various JavaScript types and objects are represented by classes in JE. Each class provides the methods listed below. In some cases, a class may throw an exception when the method is called. Note: This is going to change. I am going to remove redundant methods, and make JE::Code check for the existence of the method before calling it or throwing an exception.

If you are creating your own object classes in Perl for JavaScript to use, you can subclass JE::Object, but you don't have to. Just make sure that you provide all the methods listed below.

UPGRADING VALUES

When a value is passed to the prop and method methods of objects, and various other functions, it will be "upgraded" to a Perl object representing a JavaScript value. This is done by the upgrade method of the global object.

If the value to be upgraded is a blessed reference, it is 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

WHICH CLASSES ARE WHICH

Each built-in JavaScript class or primitive type is a Perl class underneath. Here is the (not yet) 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
  SyntaxError  JE::Object::Error::SyntaxError
  

And here are the primitive types:

  string      JE::String
  number      JE::Number
  boolean     JE::Boolean
  null        JE::Null
  undefined   JE::Undefined

METHODS

Each class provides the following methods. In some cases the method may simply die (as is the case, for instance, with the call and apply methods of non-function objects).

If you define your own classes, you must implement all the methods here, except for new, which is optional.

prop($name)

prop($name, $new_value)

Gets or sets a property. Setting a property returns the new value. The new value will be converted to a JS value automatically if it is not one already. (See "UPGRADING VALUES".) See also the prop({ ... }) usage below.

props

Returns a list of the names of enumerable properties. This is a list of Perl strings, not JE::Strings.

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.

The return value is a Perl scalar, not a JE::Boolean.

method($name, $arg1, $arg2, ...)

Invokes the specified method through the object. The arguments are automatically upgraded.

value

This returns a value that is supposed to be useful in Perl. JE::Object::Array->value, for instance, produces an array ref.

call(@args)

Runs the code associated with the object if it is a function. The arguments are automatically upgraded.

apply($obj, @args)

Runs the code associated with the object if it is a function. $obj will be passed to the function as its invocant (its 'this' value). The arguments are automatically upgraded.

construct(@args)

This only applies to function objects. This is just like calling a function in JS with the new keyword. 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 discarded, and the object (possibly modified) will be returned instead.

The rest of these are mostly for internal use:

Class->new($global_obj, @args)

The @args are in the same order that they are passed to the constructor function in JavaScript. 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.

prop({ ... })

The prop method can be called with a hash ref as its argument. In this case, the prototype chain is not searched, and values are not upgraded. 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

If any of the last three 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.

This is not supported by Arguments objects. It does not work on Array objects when the property name is an array index (an non-negative integer below 4,294,967,295).

is_readonly($property_name)

Object method.

This returns a boolean indicating whether a given property is readonly. If it doesn't exist, then the 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 prop.

typeof

Returns a Perl string containing the type of the object. Used by the JS typeof operator.

class

This applies to object classes only. It returns a Perl string containing the type of object. This is only used by the defoult JavaScript toString method. If you create your own object class without subclassing JE::Object, you should still provide the class method, so that this JS code will still work:

  YourClass.prototype.toString = Object.prototype.toString;
  (new YourClass).toString();

id

This returns a unique id for the object or primitive, used by the JavaScript === operator. This id is unique as a 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.

primitive

Returns true or false.

prototype

prototype ( $obj )

This applies to objects only, not to primitives. This method returns the prototype of the object. If $obj is specified, the prototype is set to that object first. The prop method uses this method. You should not normally need to call it yourself, unless you are subclassing JE::Object.

to_primitive($preferred_type)

to_boolean

to_string

to_number

to_object

These each perform the appropriate type conversion. $preferred_type, which is optional, must be either 'string' or 'number'.

Calling to_string or to_number on a object is not exactly the same as calling to_primitive('string') or to_primitive('number'), because the argument to to_primitive is merely a suggestion.

The last four methods in this list should not be overridden by subclasses.

global

Returns a reference to the global object.

OVERLOADED OPERATORS

All primitive classes overload the "" (stringification) operator. See each class's respective man page (both primitives and objects) for more info on overloaded ops.

SEE ALSO

JE and all the modules listed above.