gistfile1.js

(function($) {
  String.prototype.substrUntil = function(index, until, backwards) {
    var string = [];
    var regex = new RegExp(until, 'ig');
    if (backwards) index--; // reverse the caret direction, pretty much
    while(this[index]) {
      if (regex.test(this[index])) break;
      if (backwards) {
        string.unshift(this[index]);
        index--;
      } else {
        string.push(this[index]);
        index++;
      }
    }
    return string.join('');
  }
  
  $.fn.caretPos = function(element) {
    // http://www.webdeveloper.com/forum/showthread.php?t=74982
    // and many, many other references
    var pos;
    if (document.selection) {
      var sel = document.selection.createRange();
      sel.moveStart('character', this.get(0).value.length);
      pos = sel.text.length;
    } else {
      pos = this.get(0).selectionStart;
    }
    return pos;
  }
  
  $.wordAtCaret = function(element) {
    var value = $(element).val();
    var index = $(element).caretPos();
    var forward = value.substrUntil(index, ' ');
    var backward = value.substrUntil(index, ' ', true);
    return backward + forward;
  }
  $.fn.wordAtCaret = function() { return $.wordAtCaret(this.get(0)) }  
})(jQuery)