operators - || in javascript -

can please tell me || doing here

(function() { window.myapp = window.myapp || {}; window.myapp.lang = window.myapp.lang || {}; myapp.lang.extend = function(subclass, superclass) { subclass.prototype = new superclass(); }; })(); 

window.myapp = window.myapp || {}; 

it means: create window.myapp empty object if not exist.