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Re: What's a good Javascript book?

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On 2012-10-10 16:32, John G Harris wrote:
> One big problem with hash tables is that the hashing function must be
> unlikely to put most entries in one bucket, so giving lousy performance.
> Has anyone ever published rules for choosing property names that
> optimise performance ?

I don't know about published, but since some runtimes are open source,
we could just take a look at the hash functions. In the case of Rhino,
the underlying hash method for String objects is
java.lang.String.hashCode(). String values are hashed like this:

    public int hashCode() {
        int h = hash;
        if (h == 0 && count > 0) {
            int off = offset;
            char val[] = value;
            int len = count;

            for (int i = 0; i < len; i++) {
                h = 31*h + val[off++];
            }
            hash = h;
        }
        return h;
    }

http://www.docjar.com/html/api/java/lang/String.java.html#1481

So in this case, to avoid collisions you'd want to avoid property names
where the character values of the last characters are exactly 31 apart.
For example, the strings "ab" and "bC" will have the same hash value
(3105). The length of the string does not matter: "XXXXXXXXab" and
"XXXXXXXXbC" still have the same hash (1887221793).

As interesting as that may be, I don't think it has much practical
relevance for JS programming. For one thing, all current major ES
implementations in browsers are written in C++, and so will likely use a
different algorithm (I'm too lazy to dive into the v8 source now to see
which type of container is used there). For another thing, exactly how
the hash functions work is not part of their contract - the algorithm
may change at any time.

And finally, if I had to choose between nicely hashable property names
and easily understandable names, I would choose the latter. The most
common performance problems in browser scripting are DOM- and memory-
related, anyway.

At least in Java, if you want to make sure there are no collisions, use
single-letter variable names, like our Doctor :)


- stefan

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What's a good Javascript book? I Am Here <iamhereintheworld@gmail.com> - 2012-10-08 06:35 -0700
  Re: What's a good Javascript book? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-08 13:52 +0000
    Re: What's a good Javascript book? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-08 17:03 +0300
      Re: What's a good Javascript book? Tim Streater <timstreater@greenbee.net> - 2012-10-08 15:22 +0100
        Re: What's a good Javascript book? "Mel Smith" <med_cutout_syntel@aol.com> - 2012-10-08 08:56 -0600
  Re: What's a good Javascript book? Stefan Weiss <krewecherl@gmail.com> - 2012-10-08 16:11 +0200
    Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-09 10:43 +0100
      Re: What's a good Javascript book? Stefan Weiss <krewecherl@gmail.com> - 2012-10-09 13:12 +0200
        Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-10 15:32 +0100
          Re: What's a good Javascript book? Stefan Weiss <krewecherl@gmail.com> - 2012-10-10 20:13 +0200
            Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-11 14:28 +0100
      Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-09 17:56 +0100
        Re: What's a good Javascript book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-10 00:32 +0200
          Re: What's a good Javascript book? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-10-09 16:37 -0700
          Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-10 06:44 +0100
            Re: What's a good Javascript book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-10 20:09 +0200
            Re: What's a good Javascript book? Dr J R Stockton <reply1241@merlyn.demon.co.uk.invalid> - 2012-10-11 19:43 +0100
  Re: What's a good Javascript book? Gregor Kofler <usenet@gregorkofler.com> - 2012-10-08 16:21 +0200
  Re: What's a good Javascript book? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2012-10-08 07:56 -0700
  Re: What's a good [JavaScript] book? Matt McDonald <matt@fortybelow.ca> - 2012-10-08 11:38 -0400
    Re: What's a good [JavaScript] book? Matt McDonald <matt@fortybelow.ca> - 2012-10-08 11:42 -0400
      Re: What's a good [JavaScript] book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-10 00:41 +0200
  Re: What's a good Javascript book? Danny <dann90038@gmail.com> - 2012-10-08 11:57 -0700
    Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-08 20:39 +0100
  Re: What's a good Javascript book? I Am Here <iamhereintheworld@gmail.com> - 2012-10-09 06:19 -0700
    Re: What's a good Javascript book? Gregor Kofler <usenet@gregorkofler.com> - 2012-10-09 18:43 +0200
      Re: What's a good Javascript book? Gene Wirchenko <genew@ocis.net> - 2012-10-09 10:06 -0700
        Re: What's a good Javascript book? Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-09 11:43 -0700
          Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-09 20:07 +0100
          Re: What's a good Javascript book? Gene Wirchenko <genew@ocis.net> - 2012-10-09 13:40 -0700
        Re: What's a good Javascript book? Gregor Kofler <usenet@gregorkofler.com> - 2012-10-09 20:55 +0200
          Re: What's a good Javascript book? Gene Wirchenko <genew@ocis.net> - 2012-10-09 13:45 -0700
          Re: What's a good Javascript book? Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-10 04:31 -0700
      Re: What's a good Javascript book? Stefan Weiss <krewecherl@gmail.com> - 2012-10-09 20:09 +0200
        Re: What's a good Javascript book? Gregor Kofler <usenet@gregorkofler.com> - 2012-10-09 21:01 +0200
          Re: What's a good Javascript book? Gene Wirchenko <genew@ocis.net> - 2012-10-09 13:50 -0700
      Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-10 15:26 +0100
        Re: What's a good Javascript book? Tim Streater <timstreater@greenbee.net> - 2012-10-10 15:58 +0100
          Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-11 14:39 +0100
            Re: What's a good Javascript book? Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-11 06:52 -0700
              Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-11 17:13 +0100
                Re: What's a good Javascript book? Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-11 10:39 -0700
                Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-12 10:37 +0100
                Re: What's a good Javascript book? Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-12 07:11 -0700
                Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-13 10:53 +0100
                Re: What's a good Javascript book? Gene Wirchenko <genew@ocis.net> - 2012-10-12 09:49 -0700
                Re: What's a good Javascript book? Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-12 10:22 -0700
                Re: What's a good Javascript book? Gene Wirchenko <genew@ocis.net> - 2012-10-12 13:17 -0700
                Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-12 20:32 +0100
                Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-13 10:50 +0100
                Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-13 19:45 +0100
                Re: What's a good Javascript book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-13 21:55 +0200
                Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-13 21:52 +0100
                Re: What's a good Javascript book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-13 23:49 +0200
                Re: What's a good Javascript book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-13 23:57 +0200
                Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-13 23:34 +0100
                Re: What's a good Javascript book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-14 02:09 +0200
                Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-14 00:00 +0100
                Re: What's a good Javascript book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-14 01:58 +0200
                Re: What's a good Javascript book? Patricia Shanahan <pats@acm.org> - 2012-10-14 07:17 +0100
                Re: What's a good Javascript book? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-15 01:17 +0200
                Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-14 13:40 +0100
                Re: What's a good Javascript book? Gene Wirchenko <genew@ocis.net> - 2012-10-14 19:03 -0700
                Re: What's a good Javascript book? John G Harris <john@nospam.demon.co.uk> - 2012-10-15 10:42 +0100
    Re: What's a good Javascript book? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-09 22:49 +0200
  Re: What's a good Javascript book? Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-09 12:00 -0700
  Re: What's a good Javascript book? I Am Here <iamhereintheworld@gmail.com> - 2012-10-16 06:57 -0700

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