closest.js

String.prototype.closest = function(find, pos) {
  var found = -1;
  
  var cur1,cur2; cur1 = cur2 = pos;
  
  while (cur1 > 0 || cur2 <= this.length) {        
    is = this.substr(cur1, find.length);
    it = this.substr(cur2, find.length);
    
    if (is == find) return cur1;
    if (it == find) return cur2;
    
    if (cur1 > 0) cur1--;
    if (cur2 <= this.length) cur2++;
  }
  
  return -1;
};