membrane.js

function makeMembrane(){
    var revokableWrappingHandler = new Proxy.revokable({}, {
        get: function(target, name){
            return Reflect.call.bind(wrap(Reflect[name]));
        }
    });
    var revoke = revokableWrappingHandler.revoke;
    var wrappingHandler = revokableWrappingHandler.proxy;
    
    var un2wrapped = new WeakMap();
    var wrap = function wrap(x){
        if(Object(x) !== x)
            return x;
    
        var wrapped = un2wrapped.get(x);
        if(wrapped)
            return wrapped;

        wrapped = new Proxy(x, wrappingHandler);
        un2wrapped.set(x, wrapped);

        return p;
    };

    return {
        revoke: revoke,
        wrap: wrap
    };
};

On line 22, return p; should probably be return wrapped;