How do I create private members in a JS class? Example:

var NewLayer = cc.LayerColor.extend({
    _name: null,
    _age: null,
    
    ctor: function()
    {
        this._super(cc.color(200, 200, 200));
    },
    
    additionalFunction: function()
    {
        ...
    }
});

I can’t use var in this scope, and I can see _name and _age without problems.