duktape/website/api/duk_get_prop.yaml

=proto
duk_bool_t duk_get_prop(duk_context *ctx, duk_idx_t obj_index);

=stack
[ ... obj! ... key! ] -> [ ... obj! ... val! ]  (if key exists)
[ ... obj! ... key! ] -> [ ... obj! ... undefined! ]  (if key doesn't exist)

=summary
<p>Get the property <code>key</code> of a value at <code>obj_index</code>.
Return code and error throwing behavior:</p>
<ul>
<li>If the property exists, <code>1</code> is returned and <code>key</code>
    is replaced by the property value on the value stack.  However,
    if the property is an accessor, the "getter" function may throw
    an error.</li>
<li>If the property does not exist, 0 is returned and <code>key</code>
    is replaced by <code>undefined</code> on the value stack.</li>
<li>If the value at <code>obj_index</code> is not
    <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-9.10">object coercible</a>,
    throws an error.</li>
<li>If <code>obj_index</code> is invalid, throws an error.</li>
</ul>

<p>The property read is equivalent to the Ecmascript expression:</p>
<pre class="ecmascript-code">
obj[key]
</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-8.7.1">GetValue (V)</a>,
and <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-8.12.3">[[Get]] (P)</a>.
Both the target value and the <code>key</code> are coerced:</p>
<ul>
<li>The target value is automatically coerced to an object.  For instance,
    a string is converted to a <code>String</code> and you can access its
    <code>"length"</code> property.</li>
<li>The <code>key</code> 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 <code>key</code> when applicable.</p>
</ul>

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

<div include="object-can-be-any-value.html" />

=example
/* reading [global object].Math.PI */
duk_push_global_object(ctx);    /* -> [ global ] */
duk_push_string(ctx, "Math");   /* -> [ global "Math" ] */
duk_get_prop(ctx, -2);          /* -> [ global Math ] */
duk_push_string(ctx, "PI");     /* -> [ global Math "PI" ] */
duk_get_prop(ctx, -2);          /* -> [ global Math PI ] */
printf("Math.PI is %lf\n", (double) duk_get_number(ctx, -1));
duk_pop_n(ctx, 3);

/* reading a configuration value, cfg_idx is normalized
 * index of a configuration object.
 */
duk_push_string(ctx, "mySetting");
if (duk_get_prop(ctx, cfg_idx)) {
    const char *str_value = duk_to_string(ctx, -1);
    printf("configuration setting present, value: %s\n", str_value);
} else {
    printf("configuration setting missing\n");
}
duk_pop(ctx);  /* remember to pop, regardless of whether or not present */

=tags
property

=seealso
duk_get_prop_string
duk_get_prop_index

=introduced
1.0.0