JavaScript::XRay - See What JavaScript is Doing


Version 1.22


 use strict;
 use warnings;
 use JavaScript::XRay;

 # HTML page with a <head> and <body> tag and some javascript functions
 my $html_page = do { local $/; <> };

 # create a new instance
 my $jsxray = JavaScript::XRay->new();

 # to inline/filter external javascript files you'll need 'abs_uri'
 # my $jsxray = JavaScript::XRay->new( 
 #     abs_uri => $abs_url_or_local_file_path
 # );

 # use switches to change filtering behavior
 # $jsxray->switches( only => 'onData' );

 # use inlining to inline/filter external javascript files
 # $jsxray->inline_methods( 'dir1', 'dir2', \&callback, 'HTTP_GET' );

 # filter page
 print $js_xray->filter($html_page);


JavaScript::XRay is an HTML source filter. It was developed as a tool to help figure out and debug large JavaScript frameworks.

The main idea is that you hook it into your application framework and give you the ability to 'flip a switch' an inject a JavaScript function tracing console into your outgoing page.

Some of the things it does...

  • Injects an IFrame logging console

    It finds the body tag in the document and injects the IFrame just after it along with all the JavaScript to drive it. It also provides you with a logging function with the same name as your alias (defaults to jsxray)

       jsxray("Hi there");
  • Scans HTML for JavaScript functions

    For each function it finds it inserts a call to this method which logs the function call along with the value of the function arguments.

        function sum ( x, y ) {


        function sum ( x, y ) {
            jsxray( "sum( " + x + ", " + y + " )" );

    so now any call this function and its arguments will get logged to the IFrame.

  • Switches to limit what you log

    You can manually skip specific functions, choose to see only functions you specify, or match functions matching a specified string. ( see the switchs methods )

  • Provide execution counts

    Provides a method to see how often your functions are being called. This can be helpful to target which functions to refactor to increase performance.

  • Inlines external JavaScript files

    If external javascript files are referenced, they can be inlined so they'll be filtered as well.

  • Command line script 'jsxray'

    Use the command line script 'jsxray' to save and filter local HTML files to see how things work. Think reverse engineering. :)

  • Save the log for later.

    You can cut and paste the IFrame to a text file to analyze later by hand or munge the results with perl. Extremely helpful in moments when you have a lot of code executing and your just trying to get a handle on what's happening.


JavaScript::XRay->new( %hash );

Create a new instance with the following arguments

  • alias

    Think of this as a JavaScript namespace. All injeted JavaScript functions and variables are prefixed with this alias to avoid colliding with any code that currently exists on your page. It also is the prefix used for all the switches to toggle things on and off.

  • switches

    Hash reference containing switches to change filtering behavior. Actually just dereferences the hash and passes it onto the 'switches' method.

  • abs_uri

    Used to help find and filter external javascript files. It can be the absolute URL of the requested file via a webserver or the path of the file you're filtering from the command line.

  • iframe_height

    The height of your logging IFrame, defaults to 200 pixels.

  • css_inline

    Change the style of the logging IFrame via inline CSS.

  • css_external

    Change the style of the logging IFrame via an external stylesheet.

  • verbose

    Turn on verbose output (bool)


$jsxray->switches( %switches )

Switches control the behavior of which is going to be filtered and provide the ability to uncomment debugging code on the fly.

  • all (bool)

    Turn on filtering of all functions. This is the default behavior.

        all => 1
  • none (bool)

    Turn off filtering of functions. Helpful in combination with uncomment switch.

        none => 1
  • uncomment ( string1, string2, ... )

    Uncomment lines prefix with these strings. Helpful with injecting timing code, or more specific debugging code. You can deploy commented logging code to production and turn it on when your turn on filtering. Extremely helpful when diagnosing problems you can't reproduce in your development environment.

        uncomment => "DEBUG1,DEBUG3"
        uncomment => [ qw( DEBUG1 DEBUG3 ) ]

    will turn this...

        //DEBUG1 jsxray("Hey this is debug1");
        //DEBUG2 jsxray("Hey this is debug2");
        //DEBUG3 jsxray("Hey this is debug3");

    into this

        jsxray("Hey this is debug1");
        //DEBUG2 jsxray("Hey this is debug2");
        jsxray("Hey this is debug3");
  • anon (bool)

    Include filtering of anonymous functions.

        anon => 1
  • no_exec_count ( bool )

    Don't inject code that keeps track of how many times a function was called.

        no_exec_count => 1
  • only ( function1, function2, ... )

    Only filter comma separated list of functions (function1,function2,...)

        only => "processData,writeToPage"
        only => [ qw( processData writeToPage ) ]
  • skip ( function1, function2, ... )

    Skip comma separated list of functions

        skip => "formatNumber,onData"
        skip => [ qw( formatNumber onData ) ]
  • match ( /^string/ )

    Only filter functions that match string

        match => 'string'           # will result in qr/^string/
        match => qr/whatever/

$jsxray->inline_methods( @methods );


Take external javascript blocks (use src attribute) and get the javascript, filter it, and inline the code. There are currently three supported methods to do this.

  • HTTP_GET (default)

    Special string that represents using LWP::Simple to attempt to fetch external javascript. If the src attribute isn't absolute, then you'll need to pass the 'abs_uri' in when you create your instance.

  • File Directory

    Base file path to use with the src attribute to load the javascript off disk. From a webserver, you'd probably include the web root and from the commandline, you'd use the path of the file you're filtering.

  • Code Reference

    The arguments to the code reference are the src attribute from the javascript attribute and the code block must return the coresponding code.

        $javascript_code = &$code_ref( $src_attr, $abs_uri );

$jsxray->filter( $html );

Pass HTML in, get modified HTML out.


Jeff Bisbee, <jbisbee at>


Some of the things that are still in the conceptional phase

  • Personal proxy

    Include a personal proxy script with this module so you can filter ANY webpage you go to.

  • Add a user interface to the console to control the switches

    Add a form to the console that will allow you to see the values of the switches and then resubmit the url to have the changes take affect.

  • Add .toSource to objects when logging (or a switch to turn it on)


Please report any bugs or feature requests to bug-JavaScript-xray at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc JavaScript::XRay

You can also look for information at:


  • Senta Mcadoo

    Providing the JavaScript DOM logging code in order to do the reverse logging (solved the scrolling problem).

  • Ronnie Paskin

    General hacking on the code, good feedback, and for being a sounding board to work out issues.

  • Tony Fernandez

    Giving me the green light to publish this on the CPAN.


Copyright 2006 Jeff Bisbee, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.