# JSObjectCallAsFunctionCallback The callback type for calling an object as a function. ``` typealias JSObjectCallAsFunctionCallback = (JSContextRef?, JSObjectRef?, JSObjectRef?, Int, UnsafePointer?, UnsafeMutablePointer?) -> JSValueRef? ``` ## Parameters `ctx` The execution context to use. `function` A [`JSObjectRef`](/documentation/JavaScriptCore/JSObjectRef) that is the function to call. `thisObject` A [`JSObjectRef`](/documentation/JavaScriptCore/JSObjectRef) that is the `this` variable in the function’s scope. `argumentCount` An integer count of the number of arguments in `arguments`. `arguments` A `JSValue` array of the arguments to pass to the function. `exception` A pointer to a [`JSValueRef`](/documentation/JavaScriptCore/JSValueRef) to return an exception in, if any. ## Return Value A [`JSValueRef`](/documentation/JavaScriptCore/JSValueRef) that is the function’s return value. ## Discussion If you name your function `CallAsFunction`, you declare it like this: ```c JSValueRef CallAsFunction(JSContextRef ctx, JSObjectRef function, JSObjectRef thisObject, size_t argumentCount, const JSValueRef arguments[], JSValueRef* exception); ``` If the JavaScript expression `myObject.myFunction()` invokes your callback, it sets `function` to `myFunction`, and `thisObject` to `myObject`. If this callback is `NULL`, calling your object as a function throws an exception. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)