This article covers features introduced in SpiderMonkey 24

RAII helper to enter a different compartment on the given context and automatically leave it once the JSAutoCompartment instance gets out of scope.


JSAutoCompartment(JSContext *cx, JSObject *target);

JSAutoCompartment(JSContext *cx, JSScript *target);
Name Type Description
cx JSContext * The context on which a cross-compartment call is needed.
target JSObject * / JSScript *

The object in a different compartment to be accessed. This implicitly identifies the compartment to be entered.


Every JSContext has a current compartment. Only objects in the current compartment can be accessed, so to access an object in a different compartment, this containing compartment has to be entered first. Compartments have to be entered and left in LIFO order. JSAutoCompartment guarantees that by automatically entering the given compartment and leaving it upon getting out of scope:
void foo(JSContext *cx, JObject *obj) {
    // in some compartment 'c'
        JSAutoCompartment ac(cx, obj);  // constructor enters
        // in the compartment of 'obj'
    }                                 // destructor leaves
    // back in compartment 'c'

See Also