truncate a string to a set number of chars and add ellipses with respect for non-word characters.

fit.js

function fit(str, nMaxChars) {
    var n = nMaxChars - 1,
        strRX = /\s|\.|,/,
        tmp_str = str.slice(0, n),
        final_str;

    if (str.length <= n) return str;

    function getLastChar(str) {
      return str.slice(str.length-1, str.length);
    }

    function trimLastChar(str) {
      return str.slice(0, str.length - 1);
    }

    (function isLast(lstr){
      var lastChar = getLastChar(lstr),
          short_str = trimLastChar(lstr),
          short_lastChar = getLastChar(short_str);

      if( strRX.test(lastChar) ) {
        final_str = ( /\W/.test(short_lastChar) ) ? trimLastChar(short_str) : short_str;
        final_str += "...";
      } else {
        isLast(short_str);
      }
    })(tmp_str);

    return final_str;

  }

Just one thins. Needed to check the length to see if it was already <= n

if(str.length <= n) return str;

http://jsfiddle.net/tbeseda/VTPta/3/