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69 lines
2.7 KiB
69 lines
2.7 KiB
name: duk_has_prop
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proto: |
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duk_bool_t duk_has_prop(duk_context *ctx, duk_idx_t obj_idx);
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stack: |
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[ ... obj! ... key! ] -> [ ... obj! ... ]
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summary: |
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<p>Check whether value at <code>obj_idx</code> has a property <code>key</code>.
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<code>key</code> is removed from the stack. Return code and error throwing
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behavior:</p>
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<ul>
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<li>If the property exists, <code>1</code> is returned.</li>
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<li>If the property doesn't exist, 0 is returned.</li>
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<li>If the value at <code>obj_idx</code> is not an object, throws an error.</li>
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<li>If <code>obj_idx</code> is invalid, throws an error.</li>
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</ul>
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<p>The property existence check is equivalent to the Ecmascript expression
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<code>res = key in obj</code>. For semantics, see
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<a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.2.1">Property Accessors</a>,
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<a href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.8.7">The in operator</a>,
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and <a href="http://www.ecma-international.org/ecma-262/5.1/#sec-8.12.6">[[HasProperty]] (P)</a>.
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Both the target value and the <code>key</code> are coerced:</p>
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<ul>
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<li>The target value is automatically coerced to an object. For instance,
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a string is converted to a <code>String</code> and you can check for its
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<code>"length"</code> property.</li>
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<li>The <code>key</code> argument is internally coerced using ToPropertyKey()
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coercion which results in a string or a Symbol. There is an internal
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fast path for arrays and numeric indices which avoids an explicit string
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coercion, so use a numeric <code>key</code> when applicable.</li>
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</ul>
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<p>If the target is a Proxy object which implements the <code>has</code> trap,
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the trap is invoked and the API call return value matches the trap return value.</p>
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<div class="note">
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Instead of accepting any
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<a href="http://www.ecma-international.org/ecma-262/5.1/#sec-9.10">object coercible</a>
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value (like most property related API calls) this call accepts only an object
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as its target value. This is intentional as it follows Ecmascript operator semantics.
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</div>
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<p>If the key is a fixed string you can avoid one API call and use the
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<code><a href="#duk_has_prop_string">duk_has_prop_string()</a></code> variant.
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Similarly, if the key is an array index, you can use the
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<code><a href="#duk_has_prop_index">duk_has_prop_index()</a></code> variant.</p>
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<div include="object-can-be-any-value.html" />
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example: |
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duk_push_string(ctx, "myProperty");
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if (duk_has_prop(ctx, -3)) {
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printf("obj has 'myProperty'\n");
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} else {
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printf("obj does not have 'myProperty'\n");
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}
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tags:
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- property
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seealso:
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- duk_has_prop_string
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- duk_has_prop_lstring
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- duk_has_prop_index
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introduced: 1.0.0
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