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<td >Qt 5.12</td><td ><a href="qtqml-index.html">Qt QML</a></td><td >Making Applications Scriptable</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right"><a href="qtqml-index.html">Qt 5.12.6 Reference Documentation</a></td>
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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#scripting-classes">Scripting Classes</a></li>
<li class="level1"><a href="#basic-usage">Basic Usage</a></li>
<li class="level1"><a href="#making-a-qobject-available-to-the-script-engine">Making a QObject Available to the Script Engine</a></li>
<li class="level1"><a href="#implications-for-application-security">Implications for Application Security</a></li>
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<h1 class="title">Making Applications Scriptable</h1>
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<p>Qt provides support for application scripting with JavaScript. The following guides and references cover aspects of programming with JavaScript and Qt.</p>
<a name="scripting-classes"></a>
<h2 id="scripting-classes">Scripting Classes</h2>
<p>The following classes add scripting capabilities to Qt applications.</p>
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<tr class="odd topAlign"><td class="tblName"><p><a href="qjsengine.html">QJSEngine</a></p></td><td class="tblDescr"><p>Environment for evaluating JavaScript code</p></td></tr>
<tr class="even topAlign"><td class="tblName"><p><a href="qjsvalue.html">QJSValue</a></p></td><td class="tblDescr"><p>Acts as a container for Qt/JavaScript data types</p></td></tr>
<tr class="odd topAlign"><td class="tblName"><p><a href="qjsvalueiterator.html">QJSValueIterator</a></p></td><td class="tblDescr"><p>Java-style iterator for QJSValue</p></td></tr>
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<a name="basic-usage"></a>
<h2 id="basic-usage">Basic Usage</h2>
<p>To evaluate script code, you create a <a href="qjsengine.html">QJSEngine</a> and call its evaluate() function, passing the script code (text) to evaluate as argument.</p>
<pre class="cpp">
<span class="type"><a href="qjsengine.html">QJSEngine</a></span> engine;
qDebug() <span class="operator"><</span><span class="operator"><</span> <span class="string">"the magic number is:"</span> <span class="operator"><</span><span class="operator"><</span> engine<span class="operator">.</span>evaluate(<span class="string">"1 + 2"</span>)<span class="operator">.</span>toNumber();
</pre>
<p>The return value will be the result of the evaluation (represented as a <a href="qjsvalue.html">QJSValue</a> object); this can be converted to standard C++ and Qt types.</p>
<p>Custom properties can be made available to scripts by registering them with the script engine. This is most easily done by setting properties of the script engine's <i>Global Object</i>:</p>
<pre class="cpp">
engine<span class="operator">.</span>globalObject()<span class="operator">.</span>setProperty(<span class="string">"foo"</span><span class="operator">,</span> <span class="number">123</span>);
qDebug() <span class="operator"><</span><span class="operator"><</span> <span class="string">"foo times two is:"</span> <span class="operator"><</span><span class="operator"><</span> engine<span class="operator">.</span>evaluate(<span class="string">"foo * 2"</span>)<span class="operator">.</span>toNumber();
</pre>
<p>This places the properties in the script environment, thus making them available to script code.</p>
<a name="making-a-qobject-available-to-the-script-engine"></a>
<h2 id="making-a-qobject-available-to-the-script-engine">Making a QObject Available to the Script Engine</h2>
<p>Any QObject-based instance can be made available for use with scripts.</p>
<p>When a QObject is passed to the <a href="qjsengine.html#newQObject">QJSEngine::newQObject</a>() function, a Qt Script wrapper object is created that can be used to make the QObject's signals, slots, properties, and child objects available to scripts.</p>
<p>Here's an example of making an instance of a QObject subclass available to script code under the name <code>"myObject"</code>:</p>
<pre class="cpp">
<span class="type"><a href="qjsengine.html">QJSEngine</a></span> engine;
<span class="type">QObject</span> <span class="operator">*</span>someObject <span class="operator">=</span> <span class="keyword">new</span> MyObject;
<span class="type"><a href="qjsvalue.html">QJSValue</a></span> objectValue <span class="operator">=</span> engine<span class="operator">.</span>newQObject(someObject);
engine<span class="operator">.</span>globalObject()<span class="operator">.</span>setProperty(<span class="string">"myObject"</span><span class="operator">,</span> objectValue);
</pre>
<p>This will create a global variable called <code>myObject</code> in the script environment. The variable serves as a proxy to the underlying C++ object. Note that the name of the script variable can be anything; i.e., it is not dependent upon QObject::objectName().</p>
<a name="implications-for-application-security"></a>
<h2 id="implications-for-application-security">Implications for Application Security</h2>
<p>The security model of application scripting with JavaScript follows the same model as for C++ code: the user installs scripts to run that they trust in the same way as they install Qt applications.</p>
<p>In order to preserve the trust of users, application developers should not evaluate arbitrary JavaScript code. The JavaScript engine's sandbox is only a semantic barrier. The script is evaluated in the same process and with the same privileges as the rest of the application and shares the same memory. As a consequence, C++ objects exposed to scripts are accessible without additional security guards.</p>
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