duktape/website/api/duk_has_prop.txt

=proto
int duk_has_prop(duk_context *ctx, int obj_index);

=stack
[ ... obj! ... key! ] -> [ ... obj! ... ]

=summary
<p>Check whether value at <tt>obj_index</tt> has a property <tt>key</tt>.
<tt>key</tt> is removed from the stack.  Return code and error throwing
behavior:</p>
<ul>
<li>If the property exists, a non-zero value is returned.</li>
<li>If the property doesn't exist, 0 is returned.</li>
<li>If the value at <tt>obj_index</tt> is not an object, throws an error.</li>
<li>If <tt>obj_index</tt> is invalid, throws an error.</li>
</ul>

<p>The property existence check is equivalent to the Ecmascript expression:</p>
<pre class="ecmascript-code">
key in obj
</pre>

<p>For semantics, see
<a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.2.1">Property Accessors</a>,
<a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.8.7">The in operator</a>,
and <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-8.12.6">[[HasProperty]] (P)</a>.
Both the target value and the <tt>key</tt> are coerced:</p>
<ul>
<li>The target value is automatically coerced to an object.  For instance,
    a string is converted to a <tt>String</tt> and you can check for its
    <tt>"length"</tt> property.</li>
<li>The <tt>key</tt> argument is internally coerced to a string.  There is
    an internal fast path for arrays and numeric indices which avoids an
    explicit string coercion, so use a numeric <tt>key</tt> when applicable.</p>
</ul>

<div class="note">
Instead of accepting any
<a href="http://www.ecma-international.org/ecma-262/5.1/#sec-9.10">object coercible</a>
value (like most property related API calls) this call accepts only an object
as its target value.  This is intentional as it follows Ecmascript operator semantics.
</div>

<p>If the key is a fixed string you can avoid one API call and use the
<tt><a href="#duk_has_prop_string">duk_has_prop_string()</a></tt> variant.
Similarly, if the key is an array index, you can use the
<tt><a href="#duk_has_prop_index">duk_has_prop_index()</a></tt> variant.</p>

=example
int rc;

duk_push_string(ctx, "myProperty");
if (duk_has_prop(ctx, -3)) {
    printf("obj has 'myProperty'\n");
} else {
    printf("obj does not have 'myProperty'\n");
}

=tags
property
stack

=seealso
duk_has_prop_string
duk_has_prop_index