How to avoid prototype pollution in javascript?

Question

In javascript, it's possible to "override" properties or methods of Object.prototype. For example:

Object.prototype.toString = function(){
  return "some string";
};

It can break an entire application if not used carefully. Are there any tools, techniques or approaches to avoid this (for example, some kind of 'strict mode' that doesn't allow the developer to override properties of Object)?

Answer 1

Object.freeze(YourConstructor.prototype) can help protect your constructor's associated prototype object from being mucked with. From MDN:

The Object.freeze() method freezes an object: that is, prevents new properties from being added to it; prevents existing properties from being removed; and prevents existing properties, or their enumerability, configurability, or writability, from being changed, it also prevents the prototype from being changed.

It works on the object itself, rather than making a copy that's frozen. It returns the same reference you pass it.

It's best to leave built-in prototypes alone, so using it on Object.prototype and such may not be a great idea. :-) Certainly you'd need to do a lot of testing if you did... See this thread on the es-discuss mailing list for relevant, useful info.