↑
Main Page

Other ways to decrease the byte count

One of the best tools for JavaScript code minimizing and variable replacement is the ECMAScript Cruncher

(ESC) by Thomas Loo (available from Saltstorm at

http://www.saltstorm.net/depo/esc/

). ESC is a

small Windows Shell Script that can do all the optimizations mentioned in this section for you.

To run ESC, you must be using a Windows. Open up a console window and use the following format:

cscript ESC.wsf -l [0-4] -ow outputfile.js inputfile1.js [inputfile2.js]

The first part,

cscript

, is the Windows Shell Script interpreter. The filename

ESC.wsf

is the ESC pro-

gram itself. After that is the crunch level, which is a number between

and

, indicating which opti-

mizations should be applied. The

–ow

option indicates that the next argument is the output file for the

optimization. Finally, all remaining arguments are the JavaScript files to optimize. You can specify only

one file to optimize or multiple files (which are optimized and placed into the output file one after the

other).

The four levels of optimization supported by ESC are explained in the following table:

Level

Description

Leaves the script as-is. This is valuable if you want to append multiple files into a

single file.

Removes all comments.

Save as level 1, plus removes extra tabs and spaces.

Save as level 2, plus removes line breaks.

Save as level 3, plus replaces variable names.

ESC is very good at replacing variable names with nonsense names. It also is intelligent enough to

replace private object properties and methods (those denoted with two underscores at the beginning and

end of the name) with nonsense names, so your private properties and methods stay private.

ESC leaves your constructor names, public properties, and public methods intact, so no need to worry

about those. The only thing to keep in mind when using ESC is that if the JavaScript file references a

constructor in another file (such as the

StringBuffer

class from earlier in the book), crunching at level

4 replaces the references to this constructor with a nonsense name. The solution is to crunch both files

into a single file, thus retaining the constructor name.

Other ways to decrease the byte count

The following are suggestions to optimize scripts for size using somewhat uncommon methods that

save a lot of bytes. These suggestions aren’t handled by ESC, so you must carry them out by hand.

Replace Boolean values

You learned early on that for comparison purposes,

true

is equal to

and

false

is equal to

. Therefore,

anytime a script contains the literal value

true

, it can be replaced with a

and anytime a script contains

false

, it can be replaced with a

. This saves three bytes in the case of a

true

and four bytes in the case of

false

, but it doesn’t alter the meaning of any Boolean expression.

576

Chapter 19

22_579088 ch19.qxd 3/28/05 11:43 AM Page 576