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Manual Reference Pages  -  JE::OBJECT::FUNCTION (3)

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NAME

JE::Object::Function - JavaScript function class

CONTENTS

SYNOPSIS



  use JE::Object::Function;

  # simple constructors:

  $f = new JE::Object::Function $scope, @argnames, $function;
  $f = new JE::Object::Function $scope, $function;

  # constructor that lets you do anything:

  $f = new JE::Object::Function {
          name             => $name,
          scope            => $scope,
          length           => $number_of_args,
          argnames         => [ @argnames ],
          function         => $function,
          function_args    => [ $arglist ],
          constructor      => sub { ... },
          constructor_args => [ $arglist ],
          downgrade        => 0,
  };


  $f->(@args);
  $f->call_with($obj, @args);



DESCRIPTION

All JavaScript functions are instances of this class. If you want to call a JavaScript function from Perl, just treat is as a coderef ($f->()) or use the call_with method ($f->call_with($obj, @args)) if you want to specify the invocant (the ’this’ value).

OBJECT CREATION

new Creates and returns a new function (see the next few items for its usage). The new function will have a prototype property that is an object with a constructor property that refers to the function itself.

The return value of the function will be upgraded if necessary (see UPGRADING VALUES in the JE::Types man page), which is why new has to be given a reference to the global object or the scope chain. (But see also new_function in JE and new_method in JE.)

A function written in Perl can return an lvalue if it wants to. Use new JE::LValue($object, property name) to create it. To create an lvalue that refers to a variable visible within the function’s scope, use $scope->var(varname) (this assumes that you have shifted the scope object off @_ and called it $scope; you also need to call new with hashref syntax and specify the function_args [see below]).

new JE::Object::Function $scope_or_global, @argnames, $function;
new JE::Object::Function $scope_or_global, $function; $scope_or_global is one of the following:



  - a global (JE) object
  - a scope chain (JE::Scope) object



@argnames is a list of argument names, that JavaScript functions use to access the arguments.

$function is one of



  - a string containing the body of the function (JavaScript code)
  - a JE::Code object
  - a coderef



new JE::Object::Function { ... }; This is the big fancy way of creating a function that lets you do anything. The elements of the hash ref passed to new are as follows (they are all optional, except for scope):
name The name of the function. This is used only by toString.
scope A global object or scope chain object.
length The number of arguments expected. If this is omitted, the number of elements of argnames will be used. If that is omitted, 0 will be used. Note that this does not cause the argument list to be checked. It only provides the length property (and possibly, later, an arity property) for inquisitive scripts to look at.
argnames An array ref containing the variable names that a JS function uses to access the arguments.
function A coderef, string of JS code or JE::Code object (the body of the function).

This will be run when the function is called from JavaScript without the new keyword, or from Perl via the call method.

function_args This only applies when function is a code ref. function_args is an array ref, the elements being strings that indicated what arguments should be passed to the Perl subroutine. The strings, and what they mean, are as follows:



  self    the function object itself
  scope   the scope chain
  global  the global object
  this    the invocant
  args    the arguments passed to the function (as individual
          arguments)
  [args]  the arguments passed to the function (as an array ref)



If function_args is omitted, ’args’ will be assumed.

constructor A code ref that creates and initialises a new object. This is called when the new keyword is used in JavaScript, or when the construct method is used in Perl.

If this is omitted, when new or construct is used, a new empty object will be created and passed to the sub specified under function as its ’this’ value. The return value of the sub will be returned if it is an object; the (possibly modified) object originally passed to the function will be returned otherwise.

constructor_args Like function_args, but the this string does not apply. If constructor_args is omitted, the arg list will be set to [ qw( scope args ) ] (<B>this might changeB>).

This is completely ignored if constructor is omitted.

downgrade (not yet implemented) This applies only when function or constructor is a code ref. This is a boolean indicating whether the arguments to the function should have their value methods called automatically.; i.e., as though map $_->value, @args were used instead of @args.
no_proto If this is set to true, the returned function will have no prototype property.

METHODS

new JE::Object::Function See OBJECT CREATION.
call_with ( $obj, @args ) Calls a function with the given arguments. The $obj becomes the function’s invocant. This method is intended for general use from the Perl side. The arguments (including $obj) are automatically upgraded.
call ( @args ) This method, intended mainly for internal use, calls a function with the given arguments, without upgrading them. The invocant (the ’this’ value) will be the global object. This is just a wrapper around apply.

This method is very badly named and will probably be renamed in a future version. Does anyone have any suggestions?

construct This method, likewise intended mainly for internal use, calls the constructor, if this function has one (functions written in JS don’t have this). Otherwise, an 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.
apply ( $obj, @args ) This method, intended mainly for internal use just like the two above, calls the function with $obj as the invocant and @args as the args. No upgrading occurs.

This method is very badly named and will probably be renamed in a future version. Does anyone have any suggestions?

typeof This returns the string ’function’.
class This returns the string ’Function’.
value Not yet implemented.

OVERLOADING

You can use a JE::Object::Function as a coderef. The sub returned simply invokes the call method, so the following are equivalent:



  $function->call( $function->global->upgrade(@args) )
  $function->(@args)



The stringification, numification, boolification, and hash dereference ops are also overloaded. See JE::Object, which this class inherits from.

SEE ALSO

JE
JE::Object
JE::Types
JE::Scope
JE::LValue
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perl v5.20.3 JE::OBJECT::FUNCTION (3) 2014-10-20

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