Pushing literal object to empty array not working

Question

I'm trying to populate an empty array

MessageListFactory = {
    messageListCont: new Array()
}

with literal objects passed by another array as argument of this method

MessageListFactory.init = function(roomList){
    for(var i = 0; i < roomList.length; i++){
        var msgL = MessageList.create();
        msgL.init(roomList[i].jID, roomList[i].roomName);
        console.log(msgL);//Object {messages: Array[0], jID: "c1@xxxx", name: "room S1", notReadMsgCounter: 0, create: function…}
        this.messageListCont.push(msgL);//push msgL to MessageListCont
    }
    console.log(this.messageListCont);//[Object] {length: 0, __proto__: Array[0]}
    }

As you see from the console.log(), if I left the messageListCont empty, it stays as is even after the push(). But if I:

1. Put an element inside of the array before the for loop (e.g. messageListCont : ["foo"])
2. Push a string in place of the object (e.g. messageListCont.push("foo"))

In these cases, the push works and the array get populated. Anyone can explain me this?