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<li class="toctree-l2 current"><a class="current reference internal" href="#">The MathJax Object-Oriented Programming Model</a><ul>
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<div class="section" id="the-mathjax-object-oriented-programming-model">
<span id="api-object"></span><h1>The MathJax Object-Oriented Programming Model<a class="headerlink" href="#the-mathjax-object-oriented-programming-model" title="Permalink to this headline">¶</a></h1>
<p>MathJax uses an object-oriented programming model for its main
components, such as the <cite>Input jax</cite>, <cite>Output jax</cite>, and <cite>Element jax</cite>.
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 <cite>MathJax.Object</cite> or one of its subclasses, and are
instantiated by calling the object class as you would a function.</p>
<p>For example:</p>
<div class="highlight-javascript"><div class="highlight"><pre><span></span><span class="nx">MathJax</span><span class="p">.</span><span class="nb">Object</span><span class="p">.</span><span class="nx">Foo</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nb">Object</span><span class="p">.</span><span class="nx">Subclass</span><span class="p">({</span>
<span class="nx">Init</span><span class="o">:</span> <span class="kd">function</span> <span class="p">(</span><span class="nx">x</span><span class="p">)</span> <span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">setX</span><span class="p">(</span><span class="nx">x</span><span class="p">)},</span>
<span class="nx">getX</span><span class="o">:</span> <span class="kd">function</span> <span class="p">()</span> <span class="p">{</span><span class="k">return</span> <span class="k">this</span><span class="p">.</span><span class="nx">x</span><span class="p">},</span>
<span class="nx">setX</span><span class="o">:</span> <span class="kd">function</span> <span class="p">(</span><span class="nx">x</span><span class="p">)</span> <span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">x</span> <span class="o">=</span> <span class="nx">x</span><span class="p">}</span>
<span class="p">});</span>
<span class="kd">var</span> <span class="nx">foo</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nb">Object</span><span class="p">.</span><span class="nx">Foo</span><span class="p">(</span><span class="s2">"bar"</span><span class="p">);</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">getX</span><span class="p">();</span> <span class="c1">// returns "bar"</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">setX</span><span class="p">(</span><span class="s2">"foobar"</span><span class="p">);</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">getX</span><span class="p">();</span> <span class="c1">// returns "foobar"</span>
</pre></div>
</div>
<p>Object classes can have static properties and methods, which are
accessed via the object class variable. E.g.,
<code class="docutils literal"><span class="pre">MathJax.Object.Foo.SUPER</span></code> or <code class="docutils literal"><span class="pre">MathJax.Object.Foo.Augment()</span></code> for
the object in the example above. Static values are not inherited by
subclasses.</p>
<div class="section" id="static-properties">
<h2>Static Properties<a class="headerlink" href="#static-properties" title="Permalink to this headline">¶</a></h2>
<dl class="describe">
<dt>
<code class="descname">SUPER</code></dt>
<dd><p>Pointer to the super class for this subclass. (It is a reference to
<cite>MathJax.Object</cite> in the example above.)</p>
</dd></dl>
</div>
<div class="section" id="static-methods">
<h2>Static Methods<a class="headerlink" href="#static-methods" title="Permalink to this headline">¶</a></h2>
<dl class="method">
<dt id="Subclass">
<code class="descname">Subclass</code><span class="sig-paren">(</span><em>def</em><span class="optional">[</span>, <em>static</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#Subclass" title="Permalink to this definition">¶</a></dt>
<dd><p>Creates a subclass of the given class using the contents of the
<cite>def</cite> object to define new methods and properties of the object
class, and the contents of the optional <cite>static</cite> object to define
new static methods and properties.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>def</strong> — object that defines the properties and methods</li>
<li><strong>static</strong> — object that defines static properties and methods</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first last">the new object class</p>
</td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="method">
<dt id="Augment">
<code class="descname">Augment</code><span class="sig-paren">(</span><em>def</em><span class="optional">[</span>, <em>static</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#Augment" title="Permalink to this definition">¶</a></dt>
<dd><p>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.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>def</strong> — object that defines the properties and methods</li>
<li><strong>static</strong> — object that defines static properties and methods</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first last">the object class itself</p>
</td>
</tr>
</tbody>
</table>
</dd></dl>
</div>
<div class="section" id="properties">
<h2>Properties<a class="headerlink" href="#properties" title="Permalink to this headline">¶</a></h2>
<dl class="describe">
<dt>
<code class="descname">constructor</code></dt>
<dd><p>Pointer to the constructor function for this class. E.g.,
<code class="docutils literal"><span class="pre">foo.constructor</span></code> would be a reference to <code class="docutils literal"><span class="pre">MathJax.Object.Foo</span></code>
in the example above.</p>
</dd></dl>
</div>
<div class="section" id="methods">
<h2>Methods<a class="headerlink" href="#methods" title="Permalink to this headline">¶</a></h2>
<dl class="method">
<dt id="Init">
<code class="descname">Init</code><span class="sig-paren">(</span><span class="optional">[</span><em>data</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#Init" title="Permalink to this definition">¶</a></dt>
<dd><p>An optional function that is called when an instance of the class
is created. When called, the <cite>this</cite> variable is set to the newly
instantiated object, and the <cite>data</cite> is whatever was passed to the
object constructor. For instance, in the example above, the
variable <code class="docutils literal"><span class="pre">foo</span></code> is created by calling
<code class="docutils literal"><span class="pre">MathJax.Object.Foo("bar")</span></code>, which calls the
<code class="docutils literal"><span class="pre">MathJax.Object.Foo</span></code> object’s <a class="reference internal" href="#Init" title="Init"><code class="xref py py-meth docutils literal"><span class="pre">Init()</span></code></a> method with <cite>data</cite>
equal to <code class="docutils literal"><span class="pre">"bar"</span></code>. If desired, the <a class="reference internal" href="#Init" title="Init"><code class="xref py py-meth docutils literal"><span class="pre">Init()</span></code></a> method can
create a <em>different</em> object, and return that, in which case this
becomes the return value for the object constructor.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>data</strong> — the data from the constructor call</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first last"><code class="docutils literal"><span class="pre">null</span></code> or the object to be returned by the constructor</p>
</td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="method">
<dt id="isa">
<code class="descname">isa</code><span class="sig-paren">(</span><em>class</em><span class="sig-paren">)</span><a class="headerlink" href="#isa" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns <code class="docutils literal"><span class="pre">true</span></code> if the object is an instance of the given class,
or of a subclass of the given class, and <code class="docutils literal"><span class="pre">false</span></code> otherwise. So
using the <code class="docutils literal"><span class="pre">foo</span></code> value defined above,</p>
<div class="highlight-javascript"><div class="highlight"><pre><span></span><span class="nx">foo</span><span class="p">.</span><span class="nx">isa</span><span class="p">(</span><span class="nx">MathJax</span><span class="p">.</span><span class="nb">Object</span><span class="p">);</span> <span class="c1">// returns true</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">isa</span><span class="p">(</span><span class="nx">MathJax</span><span class="p">.</span><span class="nb">Object</span><span class="p">.</span><span class="nx">Foo</span><span class="p">);</span> <span class="c1">// returns true</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">isa</span><span class="p">(</span><span class="nx">MathJax</span><span class="p">.</span><span class="nx">InputJax</span><span class="p">);</span> <span class="c1">// returns false</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="can">
<code class="descname">can</code><span class="sig-paren">(</span><em>method</em><span class="sig-paren">)</span><a class="headerlink" href="#can" title="Permalink to this definition">¶</a></dt>
<dd><p>Checks if the object has the given <cite>method</cite> and returns <code class="docutils literal"><span class="pre">true</span></code>
if so, otherwise returns <code class="docutils literal"><span class="pre">false</span></code>. 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:</p>
<div class="highlight-javascript"><div class="highlight"><pre><span></span><span class="nx">foo</span><span class="p">.</span><span class="nx">can</span><span class="p">(</span><span class="s2">"getX"</span><span class="p">);</span> <span class="c1">// returns true</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">can</span><span class="p">(</span><span class="s2">"bar"</span><span class="p">);</span> <span class="c1">// returns false</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="has">
<code class="descname">has</code><span class="sig-paren">(</span><em>property</em><span class="sig-paren">)</span><a class="headerlink" href="#has" title="Permalink to this definition">¶</a></dt>
<dd><p>Checks if the object has the given <cite>property</cite> and returns <code class="docutils literal"><span class="pre">true</span></code>
if so, otherwise returns <code class="docutils literal"><span class="pre">false</span></code>. This allows you to test if an
object has a particular property available before trying to use
it. For example:</p>
<div class="highlight-javascript"><div class="highlight"><pre><span></span><span class="nx">foo</span><span class="p">.</span><span class="nx">has</span><span class="p">(</span><span class="s2">"getX"</span><span class="p">);</span> <span class="c1">// returns true</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">has</span><span class="p">(</span><span class="s2">"x"</span><span class="p">);</span> <span class="c1">// returns true</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">has</span><span class="p">(</span><span class="s2">"bar"</span><span class="p">);</span> <span class="c1">// returns false</span>
</pre></div>
</div>
</dd></dl>
</div>
<div class="section" id="accessing-the-super-class">
<h2>Accessing the Super Class<a class="headerlink" href="#accessing-the-super-class" title="Permalink to this headline">¶</a></h2>
<p>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 <code class="docutils literal"><span class="pre">arguments.callee.SUPER</span></code> refers to the super
class, so you can access any method of the superclass using that. In
order to have <cite>this</cite> refer to the current object when you call the
super class, however, you need to use <code class="docutils literal"><span class="pre">call()</span></code> or
<code class="docutils literal"><span class="pre">apply()</span></code> to access the given method.</p>
<p>For example, <code class="docutils literal"><span class="pre">arguments.callee.SUPER.method.call(this,data)</span></code> would
call the superclass’ <cite>method</cite> and pass it <cite>data</cite> as its argument,
properly passing the current object as <cite>this</cite>. Alternatively, you can
use <code class="docutils literal"><span class="pre">this.SUPER(arguments)</span></code> in place of <code class="docutils literal"><span class="pre">arguments.callee.SUPER</span></code>.
It is also possible to refer to the super class explicitly rather than
through <code class="docutils literal"><span class="pre">arguments.callee.SUPER</span></code>, as in the following example:</p>
<div class="highlight-javascript"><div class="highlight"><pre><span></span><span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class1</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nb">Object</span><span class="p">.</span><span class="nx">Subclass</span><span class="p">({</span>
<span class="nx">Init</span><span class="o">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">x</span><span class="p">)</span> <span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">x</span> <span class="o">=</span> <span class="nx">x</span><span class="p">},</span>
<span class="nx">XandY</span><span class="o">:</span> <span class="kd">function</span><span class="p">(</span><span class="nx">y</span><span class="p">)</span> <span class="p">{</span><span class="k">return</span> <span class="s2">"Class1: x and y = "</span> <span class="o">+</span> <span class="k">this</span><span class="p">.</span><span class="nx">x</span> <span class="o">+</span> <span class="s2">" and "</span> <span class="o">+</span> <span class="nx">y</span><span class="p">}</span>
<span class="p">});</span>
<span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class2</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class1</span><span class="p">.</span><span class="nx">Subclass</span><span class="p">({</span>
<span class="nx">XandY</span><span class="o">:</span> <span class="kd">function</span> <span class="p">(</span><span class="nx">y</span><span class="p">)</span> <span class="p">{</span><span class="k">return</span> <span class="s2">"Class2: "</span><span class="o">+</span><span class="nx">arguments</span><span class="p">.</span><span class="nx">callee</span><span class="p">.</span><span class="nx">SUPER</span><span class="p">.</span><span class="nx">XandY</span><span class="p">.</span><span class="nx">call</span><span class="p">(</span><span class="k">this</span><span class="p">,</span><span class="nx">y</span><span class="p">)}</span>
<span class="p">});</span>
<span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class3</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class2</span><span class="p">.</span><span class="nx">Subclass</span><span class="p">({</span>
<span class="nx">XandY</span><span class="o">:</span> <span class="kd">function</span> <span class="p">(</span><span class="nx">y</span><span class="p">)</span> <span class="p">{</span><span class="k">return</span> <span class="s2">"Class3: "</span><span class="o">+</span><span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class2</span><span class="p">.</span><span class="nx">prototype</span><span class="p">.</span><span class="nx">XandY</span><span class="p">.</span><span class="nx">call</span><span class="p">(</span><span class="k">this</span><span class="p">,</span><span class="nx">y</span><span class="p">)}</span>
<span class="p">});</span>
<span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class4</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class1</span><span class="p">.</span><span class="nx">Subclass</span><span class="p">({</span>
<span class="nx">XandY</span><span class="o">:</span> <span class="kd">function</span> <span class="p">(</span><span class="nx">y</span><span class="p">)</span> <span class="p">{</span><span class="k">return</span> <span class="s2">"Class4: "</span><span class="o">+</span><span class="k">this</span><span class="p">.</span><span class="nx">SUPER</span><span class="p">(</span><span class="nx">arguments</span><span class="p">).</span><span class="nx">XandY</span><span class="p">.</span><span class="nx">call</span><span class="p">(</span><span class="k">this</span><span class="p">,</span><span class="nx">y</span><span class="p">)}</span>
<span class="p">});</span>
<span class="kd">var</span> <span class="nx">foo</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class2</span><span class="p">(</span><span class="s2">"foo"</span><span class="p">);</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">XandY</span><span class="p">(</span><span class="s2">"bar"</span><span class="p">);</span> <span class="c1">// returns "Class2: Class1: x and y = foo and bar"</span>
<span class="kd">var</span> <span class="nx">bar</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class3</span><span class="p">(</span><span class="s2">"bar"</span><span class="p">);</span>
<span class="nx">bar</span><span class="p">.</span><span class="nx">XandY</span><span class="p">(</span><span class="s2">"foo"</span><span class="p">);</span> <span class="c1">// returns "Class3: Class2: Class1: x and y = bar and foo"</span>
<span class="kd">var</span> <span class="nx">moo</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class4</span><span class="p">(</span><span class="s2">"moo"</span><span class="p">);</span>
<span class="nx">moo</span><span class="p">.</span><span class="nx">XandY</span><span class="p">(</span><span class="s2">"cow"</span><span class="p">);</span> <span class="c1">// returns "Class4: Class1: x and y = moo and cow"</span>
</pre></div>
</div>
<p>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.</p>
<p>Since most calls to the super class are to the overridden method, not
to some other method, the method name and the <code class="docutils literal"><span class="pre">call()</span></code> are
essentially redundant. You can get a more convenient syntax by
wrapping the <cite>def</cite> for the <a class="reference internal" href="#Subclass" title="Subclass"><code class="xref py py-meth docutils literal"><span class="pre">Subclass()</span></code></a> call in a call to
<code class="docutils literal"><span class="pre">MathJax.Object.SimpleSUPER()</span></code>, as in the following example:</p>
<div class="highlight-javascript"><div class="highlight"><pre><span></span><span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class1</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nb">Object</span><span class="p">.</span><span class="nx">Subclass</span><span class="p">({</span>
<span class="nx">Init</span><span class="o">:</span> <span class="kd">function</span> <span class="p">(</span><span class="nx">x</span><span class="p">)</span> <span class="p">{</span><span class="k">this</span><span class="p">.</span><span class="nx">x</span> <span class="o">=</span> <span class="nx">x</span><span class="p">},</span>
<span class="nx">XandY</span><span class="o">:</span> <span class="kd">function</span> <span class="p">(</span><span class="nx">y</span><span class="p">)</span> <span class="p">{</span><span class="k">return</span> <span class="s2">"Class1: x and y = "</span> <span class="o">+</span> <span class="k">this</span><span class="p">.</span><span class="nx">x</span> <span class="o">+</span> <span class="s2">" and "</span> <span class="o">+</span> <span class="nx">y</span><span class="p">}</span>
<span class="p">});</span>
<span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class2</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class1</span><span class="p">.</span><span class="nx">Subclass</span><span class="p">(</span>
<span class="nx">MathJax</span><span class="p">.</span><span class="nb">Object</span><span class="p">.</span><span class="nx">SimpleSUPER</span><span class="p">({</span>
<span class="nx">XandY</span><span class="o">:</span> <span class="kd">function</span> <span class="p">(</span><span class="nx">y</span><span class="p">)</span> <span class="p">{</span><span class="k">return</span> <span class="s2">"Class2: "</span><span class="o">+</span><span class="k">this</span><span class="p">.</span><span class="nx">SUPER</span><span class="p">(</span><span class="nx">y</span><span class="p">)},</span>
<span class="nx">AnotherMethod</span><span class="o">:</span> <span class="kd">function</span> <span class="p">()</span> <span class="p">{</span><span class="k">return</span> <span class="k">this</span><span class="p">.</span><span class="nx">x</span><span class="p">}</span> <span class="c1">// it's OK if a method doesn't use SUPER</span>
<span class="p">})</span>
<span class="p">);</span>
<span class="kd">var</span> <span class="nx">foo</span> <span class="o">=</span> <span class="nx">MathJax</span><span class="p">.</span><span class="nx">Class2</span><span class="p">(</span><span class="s2">"foo"</span><span class="p">);</span>
<span class="nx">foo</span><span class="p">.</span><span class="nx">XandY</span><span class="p">(</span><span class="s2">"bar"</span><span class="p">);</span> <span class="c1">// returns "Class2: Class1: x and y = foo and bar"</span>
</pre></div>
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