Saturday, 22 August 2009

Strictly Javascript Compressor

Introducing yet another Javascript compressor

If you read a previous article about creating a script compressor you will know that I like to write my own code purely for sadistic reasons and mainly due to a rare form of OCD that makes me unable to stop coding until something is complete. I am sure this a rather common infliction amongst some in the coding community however it does have its benefits. Although creating a compressor from scratch is a long and painful process it has the upside of increasing knowledge about code syntax, compression techniques, regular expressions, language quirks and much much more. I wouldn't recommend doing it unless you have plenty of time and a desire to know the pain that regular expression based compression can bring.

The Strictly Software Javascript Compressor Tool

I have put a cut down version of my compressor tool up on my website which you can find at the following link: Strictly Javascript Compressor

The online tool only works with Javascript but I have made available a number of options which will allow you to customise the compression process.


Compression Options


The following is a list of all the advanced options available with the online version of the compressor.

Compression Modes: Simple or Complex

Complex mode will try to format the Javascript so that each function is on its own line in the output. If you have a function that contains other functions then only the outer most function will be formatted like this. To accomplish this the engine must try to auto-correct any lines that have missing terminators or brackets by inserting them. In most cases this should work but I cannot guarantee this in 100% of cases due to the engine being based on regular expressions. However if you format your code correctly before hand ensuring all lines are terminated and IF, ELSE statements are wrapped in brackets then you shouldn't get any problems.

Simple mode will not try to put each function on its own line although it will condense multiple occurrences of brackets to one line. This mode will give a longer output as it will contain more carriage returns however it will be less likely to cause syntax errors.

Complex mode will result in a better compression rate than simple mode, sometimes up to 10% or more in certain cases.

Minify Functions

If you have specific global functions that you wish to replace with smaller names then you can provide a list of the functions to replace in the format

[function:minified,function:minified]


For example if you want to replace all occurrances of the function getEl with a minified name of G and the function addEvent with the name A then you can provide a list in the format of:

[function:minified, function:minified]

[getEl:G,addEvent:A]


Important Note:
  • You can only provide 20 functions to rename with this online tool.
  • As my minification process renames long variable and parameter names in local functions with single letter versions starting from a and incrementing up to zz you should avoid using lower case letters for your minified function names to avoid clashes. Its recommended to use upper case letters or use underscores.


Minify Objects

In the same way that you can change function names you can also provide up to 20 global objects that you can replace with minified names. For example if you have global objects Debugger and System you could replace them with _D and _S respectively. Provide this list in the following format of

[object:minified, object:minified]

[Debugger:_D,System:_S]

Important Notes
  • You can only provide 20 objects to rename with this online tool.
  • As my minification process renames long variable and parameter names in local functions with single letter versions starting from a and incrementing up to zz you should avoid using lower case letters for your minified object names to avoid clashes. Its recommended to use upper case letters or use underscores.
Minify Global Objects

This option will replace some standard global objects with smaller versions. The objects it will replace are Window, Document and Navigator. The engine will add the following line of code to the output:

var _w=window,_d=document,_n=navigator


Then it will replace all occurrences of window with _w and so on. Note how I have added underscores to the variable names so not to conflict with the standard minification process of function parameters and variables.

Create a Get Function

This option will replace all occurrences of references to document.getElementById to a minified function call. As this is a very common reference in Javascript code on the web it will save considerable bytes and is very easy to do. The name of the function created will be decided by the value supplied for the Get Function Name option.

Note: If none is supplied the value will be G.

Get Function Name

This option is related to the previous option and only available if you have decided to create a Get function. The value you supply will be used for the minified function name. For example if you provide the following value _S then the following function will be created and added to the compressed output:

_S=function(i){return document.getElementById(i)}


Remove ShowDebug Functions

This maybe a very specific function catering to my own needs but its something I would recommend to all developers. As you create your code you should build in calls to a debug function that will output messages to the console (e.g Firebug, Firebug-lite, IE, Chromes console). This is a much better idea than having to add debug code once a bug has been found and it will save time in fixing the bug. However you should also remove all these functions on a live production environment as you will not want your users to view these messages and even if you turn debugging off inside the function an unnecessary call to the function is made. I always call my debug function ShowDebug. This option will remove all these calls from the code.

If you would like to know more about debugging and creating a custom debug object please read the following blog article.

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