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Create a native function and assign it as a property to a specified JS object.


JSFunction *
JS_DefineFunction(JSContext *cx, JS::Handle<JSObject*> obj,
                  const char *name, JSNative call,
                  unsigned nargs, unsigned attrs);

JSFunction *
JS_DefineUCFunction(JSContext *cx, JS::Handle<JSObject*> obj,
                    const char16_t *name, size_t namelen, JSNative call,
                    unsigned nargs, unsigned attrs);

JSFunction *
JS_DefineFunctionById(JSContext *cx, JS::Handle<JSObject*> obj,
                      JS::Handle<jsid> id, JSNative call,
                      unsigned nargs, unsigned attrs); // Added in SpiderMonkey 17
Name Type Description
cx JSContext * The context in which to define the function. Requires request. In a JS_THREADSAFE build, the caller must be in a request on this JSContext.
obj JS::Handle<JSObject*> Object for which to define a function as a property (method).
name const char * or const char16_t * Name to assign to the function.
id JS::Handle<jsid> A pointer to jsid for name to assign to the function. Added in SpiderMonkey 17
call JSNative The native C/C++ function to be wrapped by the new function.
nargs unsigned Number of arguments that are passed to the function when it is called.
flags unsigned The logical OR of zero or more property attributes.


JS_DefineFunction exposes a C/C++ function to scripts by defining a new method on an existing JavaScript object. It creates the new Function object as though by calling JS_NewFunction, then makes it a method of obj as though by calling JS_DefineProperty. JS_DefineUCFunction is the Unicode version of the function.

name is the name of the property to create in obj. That is, it is the method name that scripts can use to call the new function. It also becomes the name property of the new function object and can be accessed using JS_GetFunctionId.

call is a pointer to the C/C++ function that is to be exposed to JavaScript.

nargs indicates the number of arguments the function expects to receive. This becomes the new function object's length property and can be accessed using JS_GetFunctionArity.

flags is the logical OR of zero or more property attributes, which apply to the new property.

On success, JS_DefineFunction and JS_DefineUCFunction return a pointer to the new function. On error or exception, they return NULL.

See Also

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 Contributors to this page: arai, fscholz, Jorend, Dria, MMondor
 Last updated by: arai,