On Sep 5, 2008, at 4:33 PM, Ingvar von Schoultz wrote: > Ingvar von Schoultz skrev: >> Mark S. Miller skrev: >>> On Fri, Sep 5, 2008 at 2:33 PM, Ingvar von Schoultz >>> <[EMAIL PROTECTED]> wrote: >>>> and silent failures >>>> are often very expensive to debug. >>> I don't understand. As currently proposed, Object.freeze always >>> succeeds. What silent failure are you concerned about? >> >> If you set a property to non-configurable it means you don't >> want it reconfigured. If code is still allowed to change it >> from writable to non-writable, this is a silent failure of >> the guard against reconfiguring. > > Another silent failure, much more expensive, is when you try > to write to non-writable properties. (And, apart from this, > also the related similar problem with constant variables).
This goes back to ES1. In Netscape's original JS implementation, I reported an error which stopped the script on assignment to read-only properties (this from memory, I don't have source code for the old "Mocha" runtime). Without try/catch in ES1, this was viewed as too harsh by the TG1 group in TC39, leaving only silent-but-deadly failure to modify the lvalue (the result of the assignment expression is the unfiltered right-hand-side value, so you can't tell). This was not revisited when exception handling was added in ES3 :-(. > I would really like to know the reason for this strange problem > with non-writable properties, and try to see if there's any way > a better solution can be found than this seriously expensive > language bug. The proposed solution for ES3.1 and beyond is "use strict". /be _______________________________________________ Es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
