Extending a core language prototype is never necessary. And you never know which library will break when you do this (unless you review carefully the entire cod

Extending a core language prototype is never necessary. And you never know which library will break when you do this (unless you review carefully the entire code of all modules you use). So it is a bad practice, despite sometimes being ok. I admit that extending the String prototype is less dangerous than e.g. the Object or Array prototype.