| JE::Types(3pm) | User Contributed Perl Documentation | JE::Types(3pm) |
JE::Types - JavaScript types and objects
This is just documentation, not a module.
The various JavaScript types and objects are represented by Perl classes in JE (which are listed below). This document describes the basic interface implemented by these classes. Information specific to each class can be found on its own manual page.
When a value is passed from Perl to JavaScript, 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, and the class into which it is blessed has been bound using JE's "bind_class" method, it is wrapped up in a proxy object that provides the methods JS needs. A blessed reference whose class has not been bound will be 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
WARNING: The 'upgrading' of simple scalars (strings/numbers) and regexps is still subject to change.
To do: Make &JE::upgrade detect whether a simple scalar is a string or number.
To do: Convert Regexp objects to JE::Object::RegExp objects.
Each built-in JavaScript class or primitive type is a Perl class underneath. Here is the 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 RangeError JE::Object::Error::RangeError ReferenceError JE::Object::Error::ReferenceError SyntaxError JE::Object::Error::SyntaxError TypeError JE::Object::Error::TypeError URIError JE::Object::Error::URIError
And here are the primitive types:
string JE::String number JE::Number boolean JE::Boolean null JE::Null undefined JE::Undefined
And I might also mention a few special cases:
Global JE Math JE::Object::Math Arguments JE::Object::Function::Arguments Function scope JE::Object::Function::Call RegExp constructor JE::Object::Function::RegExpConstructor
The last three are for internal use.
Every JS data type can be used as a string, boolean or number. It works exactly as it does in JavaScript. For example:
$num = $je->eval('42');
$num2 = $je->eval('NaN');
print $num2; # prints NaN
print 0+$num2; # prints nan or NaN, depending or your system
# (or something really weird on Windows).
$zero_str = $je->eval("'0'");
print "true" if $zero_str; # prints 'true'
print "false" unless 0+$zero_str; # prints 'false'
$false = $je->eval('false');
print $false; # prints 'false'
print "false" unless $false; # also prints 'false'
To access the property of a JS object, or of the JS environment itself (i.e., a global variable), just use it as a hash ref:
$je->{String}; # gives you the String constructor function
$je->{undefined}; # the undefined value
my $obj = $je->eval('var obj = new Object; return obj');
$obj->{foo} = 'bar';
"keys" will return a list of the object's enumerable properties, including those inherited from its prototype. The following example prints 'baz foo ':
$obj = $je->eval('Object.prototype.foo="bar"; ({baz:43}) ');
print "$_ " for keys %$obj;
"exists" and "delete" act upon properties of the object itself, ignoring those of its prototype, so "exists $obj->{foo}" will return false.
To call a method on an object or primitive data type, use the "method" method:
my $number = $je->eval('42');
$number->method('toString', 16); # returns the number in hexadecimal
Just use a function as though it were a coderef:
$je->{Array}->();
If you need to specify the invocant ('this' value), use the "call_with" method:
$je->{Number}{prototype}{toString}->call_with($je->eval('42'), 16);
To convert one of the fancy objects returned by JE into a simple Perl value, use the "value" method.
$number->value; # simple Perl scalar $str->value; # likewise $obj->value; # hash ref $array->value; # array ref
Currently the "value" method of objects and arrays is not recursive, but I plan to make it so later on. The only way to get consistent behaviour between this and future versions is to pass "recursive => 0" as arguments.
If you are going to write your own custom data types, proxy objects, or subclasses of JE's classes, you'll need to read this. If not, you shouldn't need to, but you might like to anyway. :-)
Be warned that some of the methods described here can be hard to use, and can easily result in code that's hard to debug, if misused. This applies to those that expect their arguments already to be objects compatible with the JE::Types interface. If you are not sure that a value you have is such, run it through the global object's "upgrade" method (or just use the "PUBLIC API", above).
These are the methods that the JavaScript engine itself uses (as opposed to those provided for convenient access from the Perl side). Each class provides whichever of the following methods are applicable. If an object does not support a particular method, a TypeError will be thrown when JavaScript code (indirectly) tries to call that method. (For instance, "'some_string'()" will attempt to call the "call" method of JE::String, thus resulting in a TypeError).
The new value is expected already to be an object compatible with the JE::Types interface.
JE::Object will also take a second argument, that allows one to indicate whether an undeletable property should be deleted. This is required by custom classes if the object in question is the global object.
The return value is a Perl scalar, not a JE::Boolean.
To do: Implement this method in subclasses of JE::Object.
YourClass.prototype.toString = Object.prototype.toString;
(new YourClass).toString();
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.
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 of JE::Object.
$taint_brush will always be a tainted empty string. If the object's internal value is not tainted, this method should return a tainted clone of the object. Otherwise, it should return the object itself.
JE and all the modules listed above under "WHICH CLASSES ARE WHICH".
| 2021-01-08 | perl v5.32.0 |