The purpose of this ditty is to truncate URIs in a more elegant way. ** I'm not a regex pro, be gentle :)

truncateURI.js

// truncate URIs in a more elegant way
String.prototype.truncateURI = function(n, backup){
  
  var len = this.length;
  var self = this.toString();
  var max_len  = (n||30);
  var fallback = (backup||"website")
  
  var patt = /^(https?\:\/\/)?(www\.)?([a-z0-9\-\_]+)([a-z\.]{2,})+([a-z0-9\-\_\#\/ ]+\/)?([a-z0-9\-\_\#\/]+\.?[a-z0-9]+)?/i
  /*** PATTERN BREAKDOWN ***

  // only handles relatively simple URIs for now
  $0  everything        
  $1  scheme            =  ^(https?\:\/\/)?
  $2  www ?             =   (www\.)?
  $3  domain name       =   ([a-z0-9]+)
  $4  domain suffix     =   ([a-z\.]{2,})+
  $5  path(s)           =   ([a-z0-9\/ ]+\/)?
  $6  final file/path   =   ([a-z0-9]+\.[a-z0-9]+)?
      case insensitive  =  /i

  ::[todo]::
  - queries & parameters
  - more complex URIs
  */  
 
  // no truncation necessary
  if(max_len >= len) return self;

  // in case some unforseen URI gets passed in. We don't want everything to break;
  try {
    /** Step 1 **
    try stripping protocol first */
    if(self.replace(patt,"$2$3$4$5$6").length <= max_len){
      return self.replace(patt,"$2$3$4$5$6");
    } 

    /** Step 2 **
    then try stripping wwww */
    else if(self.replace(patt,"$3$4$5$6").length <= max_len){
      return self.replace(patt,"$3$4$5$6");
    }

    /** Step 3 **
    then replace filepath with /.../ */
    else if(self.replace(patt,"$3$4/.../$6").length <= max_len){
      return self.replace(patt,"$3$4/.../$6");
    }

    /** Step 4 **
    then strip final file/path */
    else if(self.replace(patt,"$3$4/...").length <= max_len){
      return self.replace(patt,"$3$4/...");
    }

    /** Step 5 **
    then strip domain suffix */
    else if(self.replace(patt,"$3").length <= max_len){
      return self.replace(patt,"$3");
    }

    /** Step 6 **
    Give up & return "website" instead of original URL */
    else {
      return fallback;
    }
  } catch(err){
    console.log(err);
    return self;
  }
}