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<td >Qt 5.12</td><td ><a href="qtscript-index.html">Qt Script</a></td><td >Creating Qt Script Extensions</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right"><a href="qtscript-index.html">Qt 5.12.6 Reference Documentation</a></td>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#static-extensions">Static Extensions</a></li>
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<h1 class="title">Creating Qt Script Extensions</h1>
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<p>Qt Script extensions can make additional functionality available to scripts evaluated by a <a href="qscriptengine.html">QScriptEngine</a>. Extensions are imported by calling the <a href="qscriptengine.html#importExtension">QScriptEngine::importExtension</a>() function.</p>
<p>There are three ways to create an extension:</p>
<ul>
<li>Subclass <a href="qscriptextensionplugin.html">QScriptExtensionPlugin</a> and implement the desired functionality.</li>
<li>Implement the functionality in a script file.</li>
<li>Use a hybrid approach, where part of the functionality is implemented in a <a href="qscriptextensionplugin.html">QScriptExtensionPlugin</a>, and part is implemented in a script file.</li>
</ul>
<p>The (dot-qualified) extension name is used to determine the path (relative to the application's plugin path) where <a href="qscriptengine.html">QScriptEngine</a> will look for the script file that will initialize the extension; if a file called <code>__init__.js</code> (usually located in <code>[application plugin path]/script/foo/</code>) is found in the corresponding folder, its contents will be evaluated by the engine when the extension is imported. As an example, if the extension is called <code>"foo.bar.baz"</code>, the engine will look for <code>__init__.js</code> in <code>foo/bar/baz</code>. Additionally, before importing <code>"foo.bar.baz"</code>, the engine will ensure that the extensions <code>"foo"</code> and <code>"foo.bar"</code> are imported, locating and evaluating the corresponding <code>__init__.js</code> in the same manner (in folders <code>foo</code> and <code>foo/bar</code>, respectively).</p>
<p>The contents of <code>__init__.js</code> are evaluated in a new <a href="qscriptcontext.html">QScriptContext</a>, as if it were the body of a function. The engine's Global Object acts as the <code>this</code> object. The following local variables are initially available to the script:</p>
<ul>
<li><b>__extension__</b>: The name of the extension (e.g. <code>"foo.bar.baz"</code>).</li>
<li><b>__setupPackage__</b>: A convenience function for setting up a "namespace" in the script environment. A typical application is to call <code>__setupPackage__()</code> with <code>__extension__</code> as argument; e.g. <code>__setupPackage__("foo.bar.baz")</code> would ensure that the object chain represented by the expression <code>foo.bar.baz</code> exists in the script environment. (This function is semantically equivalent to <a href="qscriptextensionplugin.html#setupPackage">QScriptExtensionPlugin::setupPackage</a>().)</li>
<li><b>__postInit__</b>: By default, this variable is undefined. If you assign a function to it, that function will be called <b>after</b> the C++ plugin's initialize() function has been called. You can use this to perform further initialization that depends on e.g. native functions that the C++ plugin registers.</li>
</ul>
<p>An example of a simple <code>__init__.js</code>:</p>
<pre class="js">
print("importing " + __extension__);
__setupPackage__("cool.stuff");
cool.stuff.add = function(a, b) { return a + b; }
cool.stuff.subtract = function(a, b) { return a - b; }
</pre>
<p><a href="qscriptengine.html">QScriptEngine</a> will look for a <a href="qscriptextensionplugin.html">QScriptExtensionPlugin</a> that provides the relevant extension by querying each plugin for its keys() until a match is found. The plugin's initialize() function will be called <b>after</b> the relevant <code>__init__.js</code> (if any) has been evaluated.</p>
<p>Continuining with the example of our imaginary extension <code>"foo.bar.baz"</code>, the following steps will be performed by <a href="qscriptengine.html#importExtension">QScriptEngine::importExtension</a>():</p>
<ul>
<li>If it exists, <code>foo/__init__.js</code> is evaluated.</li>
<li>If a plugin with <code>"foo"</code> in its list of keys is found, its initialize() function is called with <code>"foo"</code> as key.</li>
<li>If it exists, <code>foo/bar/__init__.js</code> is evaluated.</li>
<li>If a plugin with <code>"foo.bar"</code> in its list of keys is found, its initialize() function is called with <code>"foo.bar"</code> as key.</li>
<li>If it exists, <code>foo/bar/baz/__init__.js</code> is evaluated.</li>
<li>If a plugin with "foo.bar.baz" in its list of keys is found, its initialize() function is called with <code>"foo.bar.baz"</code> as key.</li>
</ul>
<a name="static-extensions"></a>
<h2 id="static-extensions">Static Extensions</h2>
<p>When an extension is compiled and linked into your application as a static plugin, Qt Script will look for the optional <code>__init__.js</code> script in a resource, prefixed by <code>:/qtscriptextension</code>. For example, if the extension key is "foo.bar", Qt Script will evaluate the contents of the file <code>:/qtscriptextension/foo/bar/__init__.js</code>, if it exists. Note that if the resource is built into the plugin, you may need to use the Q_INIT_RESOURCE() macro to initialize the resource before importing the extension.</p>
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