Javascript String trunc(n,useWordBoundary)

String.prototype.trunc = function(n,useWordBoundary){
  var toLong = this.length>n,
  s_ = toLong ? this.substr(0,n-1) : this;
  s_ = useWordBoundary && toLong ? s_.substr(0,s_.lastIndexOf(' ')) : s_;
  return toLong ? s_ : s_;
};