visibility.js

function A() {
  // private
  var _foo = "foo";

  function foo() {
    return _foo;
  };

  // public
  this._bar = "bar";
  this.bar = function() {
    return this._bar;
  }

  // public method returning private attribute
  this.baz = function() {
    return _foo;
  }
}

var a = new A;
a.foo()
=> TypeError: a.foo is not a function
a._foo
=> "undefined"
a.bar()
=> "bar"
a._bar
=> "bar"
a.baz()
=> "foo"

// static method
A.parse = function() { … }

var a = new A
a.parse()
// TypeError: a.parse is not a function