Type Definition ul_sys::JSObjectHasPropertyCallback

type JSObjectHasPropertyCallback = Option<unsafe extern "C" fn(ctx: JSContextRef, object: JSObjectRef, propertyName: JSStringRef) -> bool>;

@typedef JSObjectHasPropertyCallback @abstract The callback invoked when determining whether an object has a property. @param ctx The execution context to use. @param object The JSObject to search for the property. @param propertyName A JSString containing the name of the property look up. @result true if object has the property, otherwise false. @discussion If you named your function HasProperty, you would declare it like this:

bool HasProperty(JSContextRef ctx, JSObjectRef object, JSStringRef propertyName);

If this function returns false, the hasProperty request forwards to object's statically declared properties, then its parent class chain (which includes the default object class), then its prototype chain.

This callback enables optimization in cases where only a property's existence needs to be known, not its value, and computing its value would be expensive.

If this callback is NULL, the getProperty callback will be used to service hasProperty requests.