JS InstanceOf

From MDC

Determines if an object is an instance of a specified JS class.

[edit] Syntax

JSBool JS_InstanceOf(JSContext *cx, JSObject *obj,
    JSClass *clasp, jsval *argv);

Name	Type	Description
cx	JSContext *	Pointer to a JS context from which to derive runtime information. Requires request. (In a JS_THREADSAFE build, the caller must be in a request on this JSContext.)
obj	JSObject *	Object to test.
clasp	JSClass *	Class against which to test the object.
argv	jsval *	Optional argument vector. If non-null, report an error if obj is not of type clasp. argv must be the argv argument passed from the engine to a JSNative callback, JS_ARGV(cx, rv) in a JSFastNative callback, or NULL.

[edit] Description

JS_InstanceOf determines if a specified JS object, obj, has a JS class struct, clasp. If the object's internal class pointer corresponds to clasp, this function returns JS_TRUE, indicating that the object is an instance of the class. Otherwise, JS_InstanceOf returns JS_FALSE.

If argv is non-null and obj is not an instance of clasp, this function may report a class mismatch before returning. To do so, JS_InstanceOf tests whether or not there is a function name associated with the argument vector. If so, it reports the name in an error message using the JS_ReportError function.

Note that JS_InstanceOf is not the equivalent of the JavaScript instanceof keyword, which examines constructor properties along the prototype chain. JS_HasInstance is similar to instanceof.

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