From Mozilla: An overview of the object-oriented capabilities of JavaScript. This covers OO concepts of classes and objects, instances, abstraction, encapsulation and polymorphism as done in JavaScript with functions and prototypal inheritance.
Tim explains object orientation in the context of JavaScript, covering concepts like object literal, encapsulation, inheritance using prototype, composition through association and aggregation, polymorphism. Useful read for OO-aware developers to grasp some of the potential of JavaScript.