@@can.offValue( handler(newValue) )

The @@can.offValue symbol points to a function that unregisters handler from being called when the object's value changes.

var obj = function(value) {
    if(arguments.length >= 1) {
        obj.currentValue = value;
        obj.handlers.forEach(function(handler){
            handler.call(obj, value);
        });
    } else {
        return obj.currentValue;
    }
};

obj[canSymbol.for("can.offValue")] = function(handler){
    if(!obj.handlers) {
        obj.handlers = [];
    }
    obj.handlers.splice(obj.handlers.indexOf(handler), 1);
}