Attention
Version 3 is now the current version of MathJax. This document is for version 2.
The MathJax Object-Oriented Programming Model¶
MathJax uses an object-oriented programming model for its main components, such as the Input jax, Output jax, and Element jax. The model is intended to be light-weight and is based on JavaScript’s prototype inheritance mechanism. Object classes are created by making subclasses of MathJax.Object or one of its subclasses, and are instantiated by calling the object class as you would a function.
For example:
MathJax.Object.Foo = MathJax.Object.Subclass({
Init: function (x) {this.setX(x)},
getX: function () {return this.x},
setX: function (x) {this.x = x}
});
var foo = MathJax.Object.Foo("bar");
foo.getX(); // returns "bar"
foo.setX("foobar");
foo.getX(); // returns "foobar"
Object classes can have static properties and methods, which are
accessed via the object class variable. E.g.,
MathJax.Object.Foo.SUPER
or MathJax.Object.Foo.Augment()
for
the object in the example above. Static values are not inherited by
subclasses.
Static Properties¶
- SUPER
Pointer to the super class for this subclass. (It is a reference to MathJax.Object in the example above.)
Static Methods¶
- Subclass(def[, static])¶
Creates a subclass of the given class using the contents of the def object to define new methods and properties of the object class, and the contents of the optional static object to define new static methods and properties.
- Parameters:
def — object that defines the properties and methods
static — object that defines static properties and methods
- Returns:
the new object class
- Augment(def[, static])¶
Adds new properties and methods to the class prototype. All instances of the object already in existence will receive the new properties and methods automatically.
- Parameters:
def — object that defines the properties and methods
static — object that defines static properties and methods
- Returns:
the object class itself
Properties¶
- constructor
Pointer to the constructor function for this class. E.g.,
foo.constructor
would be a reference toMathJax.Object.Foo
in the example above.
Methods¶
- Init([data])¶
An optional function that is called when an instance of the class is created. When called, the this variable is set to the newly instantiated object, and the data is whatever was passed to the object constructor. For instance, in the example above, the variable
foo
is created by callingMathJax.Object.Foo("bar")
, which calls theMathJax.Object.Foo
object’sInit()
method with data equal to"bar"
. If desired, theInit()
method can create a different object, and return that, in which case this becomes the return value for the object constructor.- Parameters:
data — the data from the constructor call
- Returns:
null
or the object to be returned by the constructor
- isa(class)¶
Returns
true
if the object is an instance of the given class, or of a subclass of the given class, andfalse
otherwise. So using thefoo
value defined above,foo.isa(MathJax.Object); // returns true foo.isa(MathJax.Object.Foo); // returns true foo.isa(MathJax.InputJax); // returns false
- can(method)¶
Checks if the object has the given method and returns
true
if so, otherwise returnsfalse
. This allows you to test if an object has a particular function available before trying to call it (i.e., if an object implements a particular feature). For example:foo.can("getX"); // returns true foo.can("bar"); // returns false
- has(property)¶
Checks if the object has the given property and returns
true
if so, otherwise returnsfalse
. This allows you to test if an object has a particular property available before trying to use it. For example:foo.has("getX"); // returns true foo.has("x"); // returns true foo.has("bar"); // returns false
Accessing the Super Class¶
If a subclass overrides a method of its parent class, it may want to
call the original function as part of its replacement method. The
semantics for this are a bit awkward, but work efficiently. Within a
method, the value arguments.callee.SUPER
refers to the super
class, so you can access any method of the superclass using that. In
order to have this refer to the current object when you call the
super class, however, you need to use call()
or
apply()
to access the given method.
For example, arguments.callee.SUPER.method.call(this,data)
would
call the superclass’ method and pass it data as its argument,
properly passing the current object as this. Alternatively, you can
use this.SUPER(arguments)
in place of arguments.callee.SUPER
.
It is also possible to refer to the super class explicitly rather than
through arguments.callee.SUPER
, as in the following example:
MathJax.Class1 = MathJax.Object.Subclass({
Init: function(x) {this.x = x},
XandY: function(y) {return "Class1: x and y = " + this.x + " and " + y}
});
MathJax.Class2 = MathJax.Class1.Subclass({
XandY: function (y) {return "Class2: "+arguments.callee.SUPER.XandY.call(this,y)}
});
MathJax.Class3 = MathJax.Class2.Subclass({
XandY: function (y) {return "Class3: "+MathJax.Class2.prototype.XandY.call(this,y)}
});
MathJax.Class4 = MathJax.Class1.Subclass({
XandY: function (y) {return "Class4: "+this.SUPER(arguments).XandY.call(this,y)}
});
var foo = MathJax.Class2("foo");
foo.XandY("bar"); // returns "Class2: Class1: x and y = foo and bar"
var bar = MathJax.Class3("bar");
bar.XandY("foo"); // returns "Class3: Class2: Class1: x and y = bar and foo"
var moo = MathJax.Class4("moo");
moo.XandY("cow"); // returns "Class4: Class1: x and y = moo and cow"
Since both of these mechanisms are rather awkward, MathJax provides an alternative syntax that is easier on the programmer, but at the cost of some inefficiency in creating the subclass and in calling methods that access the super class.
Since most calls to the super class are to the overridden method, not
to some other method, the method name and the call()
are
essentially redundant. You can get a more convenient syntax by
wrapping the def for the Subclass()
call in a call to
MathJax.Object.SimpleSUPER()
, as in the following example:
MathJax.Class1 = MathJax.Object.Subclass({
Init: function (x) {this.x = x},
XandY: function (y) {return "Class1: x and y = " + this.x + " and " + y}
});
MathJax.Class2 = MathJax.Class1.Subclass(
MathJax.Object.SimpleSUPER({
XandY: function (y) {return "Class2: "+this.SUPER(y)},
AnotherMethod: function () {return this.x} // it's OK if a method doesn't use SUPER
})
);
var foo = MathJax.Class2("foo");
foo.XandY("bar"); // returns "Class2: Class1: x and y = foo and bar"