Overview

This page explains ways to reduce and/or compress the pas2js generated JavaScript.

For a complete list of optimizations, including ideas not yet implemented, see Pas2js optimizations

Omit unneeded code

• Use pas2js option -Jc to generate one JavaScript program. This allows the compiler to use Whole Program Optimization (wpo) to determine all unused identifiers.
• Use -O1 to omit unused identifiers. If a record/class is used, every unused member/method is omitted.
• By default published properties/methods are kept and will generate type information (RTTI). If you don't need that you can ...
  • use {$modeswitch omitrtti} (since pas2js 1.1), which treats class section 'published' as 'public' and typeinfo() does not work on symbols declared with this switch.
  • use -OoRemoveNotUsedPublished to omit all published properties not referenced at compile time.

Third party minifier

There are several free minifiers for JavaScript. A minifier removes unneeded characters and replaces some code without changing its functionality.

Sourcemaps: Keep in mind that third party minifiers usually makes the source map of pas2js unusable, so use the third party minifier only for the release version.

As an example here is how to use uglifyjs with pas2js:

Windows

• Download and install "node" form https://nodejs.org/en/download/
• Start the "Node.js command prompt". This starts a console, which is setup with an environment for Node.js and npm.
• In the prompt type

npm install uglify-js -g

and press <enter> This will download and install uglifyjs as a command line app. Test it by typing

uglifyjs -h

This should give the list of uglifyjs options.

• After install restart applications like Lazarus so they get the new PATH, which is needed by uglifyjs to work.
• Find out the path of uglifyjs.cmd, for example by typing where uglifyjs
• In Lazarus:
  • With pas2js 1.1: Add to the custom compiler options "-JpcmdC:\path\of\uglifyjs.cmd". Note that -Jpcmd is case sensitive.
  • With pas2js 1.0: Set the Execute After command: C:\path\of\uglifyjs.cmd -oproject1.js project1.js. Replace project1.js with the name of your js file.

Linux/MacOS

• Install npm
• Open a terminal and do:

sudo npm install uglify-js -g

This will download and install uglifyjs as a command line app. Test it by typing

uglifyjs -h

This should give the list of uglifyjs options.

• In Lazarus:
  • With pas2js 1.1: Add to the custom compiler options -Jpcmduglifyjs. This is the option -Jpcmd plus the path to uglifyjs.
  • With pas2js 1.0: Set the Execute After command: uglifyjs -oproject1.js project1.js. Replace project1.js with the name of your js file.

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From the Free Pascal wiki, page "pas2js minifier", as it stood on 2021-03-28 after a change by Mattias2, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.