user3326: Preferably written in javascript, but the language really doesn't matter.

user8309: Garbochess-JS is written in javascript.  It's about 75KB, 2400 or so lines of code I believe.  The version written in C++ was rated around 2575 on CCRL.
https://github.com/glinscott/Garbochess-JS
Lozza-js is rated around 2300, and is about twice the size of Garbochess-JS.
Toledo Nanochess and P4wn are probably less than 2000 elo, and Stockfish-js is considerably larger than Garbochess and Lozza.

user825: I'm not aware of any "small" chess engine written in JavaScript, but there's a "small" engine written in C. Micro-max has about 1900 to 2000 rating, depends on the rating list and testing condition.
http://www.computerchess.org.uk/ccrl/4040/cgi/engine_details.cgi?print=Details+%28text%29&eng=Micro-Max%204.8
Note that it's not the smallest engine, but the engine that is even smaller than Micro-max plays awful chess (dropping pieces) and even walk into check (illegal move).

3326: <p>Preferably written in javascript, but the language really doesn't matter.</p>
 8309: <p>Garbochess-JS is written in javascript.  It's about 75KB, 2400 or so lines of code I believe.  The version written in C++ was rated around 2575 on CCRL.</p>

<p><a href="https://github.com/glinscott/Garbochess-JS" rel="nofollow">https://github.com/glinscott/Garbochess-JS</a></p>

<p>Lozza-js is rated around 2300, and is about twice the size of Garbochess-JS.</p>

<p>Toledo Nanochess and P4wn are probably less than 2000 elo, and Stockfish-js is considerably larger than Garbochess and Lozza.</p>
 825: <p>I'm not aware of any "small" chess engine written in JavaScript, but there's a "small" engine written in C. Micro-max has about 1900 to 2000 rating, depends on the rating list and testing condition.</p>

<p><a href="http://www.computerchess.org.uk/ccrl/4040/cgi/engine_details.cgi?print=Details+%28text%29&amp;eng=Micro-Max%204.8" rel="nofollow">http://www.computerchess.org.uk/ccrl/4040/cgi/engine_details.cgi?print=Details+%28text%29&amp;eng=Micro-Max%204.8</a></p>

<p>Note that it's not the smallest engine, but the engine that is even smaller than Micro-max plays awful chess (dropping pieces) and even walk into check (illegal move).</p>
