Revisiting extending native prototypes after ECMAScript 5

Question

Recently, given the changes to defining properties in ECMAScript 5, I have revisited the question of whether we can safely extend the native JavaScript prototypes. In truth

Answer 1

The definitive, absolute answer is ...

"It depends." :)

Extending any built in JavaScript object can be perfectly safe or it can be a complete disaster. It depends on what you are doing and how you are doing it.

Use smart practices and common sense and test the hell-out-of-it.