696255 - object.prototype ruined with watch and unwatch

Status: RESOLVED DUPLICATE of bug 774645

(Core :: JavaScript Engine, defect)

Description

[John Smart]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:7.0.1) Gecko/20100101 Firefox/7.0.1
Build ID: 20110928134238

Steps to reproduce:

Mozilla broke Prescreen.com by adding "watch" to the object prototype.

Many JavaScript users will use {} as as key/value data-type. I used {} to store names of the elements I was putting inside of a collection.  One of these elements happened to have a user-defined name of "watch."  

var elements = {};
...
if (!elements['watch']) {
    elements['watch'] = element;
}


Actual results:

Native objects have "watch" and "unwatch" symbols attached to them, which breaks code.


Expected results:

There are millions of JavaScript programs that rely on {} to have a clean prototype.  Deciding for these users that "watch" and "unwatch" are suitable "extensions" is a poor implementation decision.  Mozilla is taking a gamble that this extremely common symbol name will not result in a namespace collision. 

If default extensions are required, please consider a namespace such as __SYMBOL__, which will not likely be used by ordinary users.

Comment 1

[John Smart]

Here is the documentation of "watch"
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/watch

Comment 2

[John Smart]

Other examples of users being confused by this "gotcha" introduced by Mozilla:

http://stackoverflow.com/questions/3269812/how-can-i-use-the-string-watch-as-a-key-in-a-javascript-associative-array

http://blog.ryanrampersad.com/2010/06/25/missing-argument-1-when-calling-function-mutator-call/

Comment 3

[Andreas Gal :gal]

watch/unwatch are **** and on the way out. However, what you are doing is colliding with other standard names as well. The right way of using objects as a hash map is:

var map = Object.create(null);

That way you won't pollute your map with prototype properties.

If you want to get rid of watch immediately, we should take that to the dev-platform mailing list. I think its hard because it will break web content. We have to do it slowly and carefully. The rest of your bug is more on your side I think, so I will close this as invalid. Use the code above instead.

Comment 4

[John Smart]

I disagree w/ this resolution.  Object.create was introduced in JavaScript 1.8.5, and I *could* use Object.create(null) if I knew that my scripts were always being invoked in JS 1.8.5.  What is the suggested solution for the other 90% of users who are not running JavaScript 1.8.5?

It seems to me that Object.create fixes the issue by just making it worse -- adding additional symbols to the root prototype and requiring detection code to work-around.