NOTE: I've completely changed the way this works for better scaling support.

NOTE: For long words/strings, you can pass a second argument to scale the results.
      Example: Soundex('Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.',true);
      Returns: L6512534623532522336312252435453 // 32 chars long: ~~(length*2/3.5)

      To provide MySQL compatability, I've added a third argument:
      Example: Soundex('Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.',true,true);
      Returns: L6512534623532523631252435453635 // 32 chars long, build length.
      MySQL:   SELECT SOUNDEX('Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.'); 

Node.js:
   var Soundex = require('soundex');
   console.log('Euler: '+Soundex('Euler')+' - Ellery: '+Soundex('Ellery'));
   console.log('Hilbert: '+Soundex('Hilbert')+' - Heilbronn: '+Soundex('Heilbronn'));
   console.log('Lukasiewicz: '+Soundex('Lukasiewicz')+' - Lissajous: '+Soundex('Lissajous'));
   console.log('(default) Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.\n'+
             Soundex('Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.',true));
   console.log('(MySQL) Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.\n'+
             Soundex('Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.',true,true));

Browser:
   <script src="./soundex.js"></script>
   <script>
      alert('Euler: '+Soundex('Euler')+' - Ellery: '+Soundex('Ellery'));
      alert('Hilbert: '+Soundex('Hilbert')+' - Heilbronn: '+Soundex('Heilbronn'));
      alert('Lukasiewicz: '+Soundex('Lukasiewicz')+' - Lissajous: '+Soundex('Lissajous'));
      alert('(default) Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.\n'+
             Soundex('Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.',true));
      alert('(MySQL) Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.\n'+
             Soundex('Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nulla interdum.',true,true));
   </script>