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Learning Dojo: Compression

By default, build compresses any packaged resources and does not compress any other resources. Both of these behaviros can be controlled by the command-line options layerOptimize( for packaged resources) and optimize( for all other resources). The possible values for these options are as follows.

  • "" Don't compress
  • shrinksafe: Use Dojo-Rhino to delete whitespace and comments and shorten variable names
  • shrinksafe.keeplines: Same as shrinksafe, but keep newlines.
  • packer: Use the Dean Edwards packer.
Whenever build compresses a resource, it writes both an uncompressed version to module-name.js.uncompressed.js and a compressed version to module-name.js

Compressing javaScript Resources with Dojo-Rhino
Dojo-Rhino walks a Rhino-generated parse tree and dumps compressed JavaScript code. The compression function can be called from the command line to compress an individual file. This technique for compressing JavaScript is both powerful and safe. Since the  routines that execute the compression are working off the parse tree, the compression is based on semantic algorithms rather than pattern matching. Consequently, obscure transformation errors are unlikely; this is not alway the case when the script is compressed by applying pattern matching algorithms.

The compression algorithms remove whitespace and comments and shorten variables names. This means that the output is still valid JavaScript source codes; specifically, there is no decompressor required to unpacke the source. The compression rate will vary greatly depending upon the input. 


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