Smarter Preprocessor

A smarter preprocessor for Node.js.

• License: MIT
• Current status: alpha

Smarter Preprocessor allows you to preprocess a Javascript module, to build modified versions of the module, or even load a modified version of the module at run-time (module.preprocessorRequire()).

But instead of adding preprocessor commands that would turn your code into non-Javascript, or hide them behind comment marks, the great idea behind Smarter Preprocessor is that preprocessor commands ARE actual Javascript code, and that that your code would run fine without even preprocessing it, falling back to default behavior.

It is a strong recommandation to keep it operational without preprocessing.

Common use cases:

• you want a lot of logs in development mode, but you don't even want that the production code had to filter them out with dozens of if statements.

• your source code uses specific features of an engine, but you have specified an alternative code that is compatible with another.

• you have some server code that works fine, you want to build a browser-compatible version

Be sure to check the recommendations.

smarter-preprocessor: the CLI program

Smarter Preprocessor can be invoked as a Command Line utility to build an alternative version of your code.

After installing it globally, using npm install -g smarter-preprocessor, we can run it from everywhere.

The syntax is simple:

smarter-preprocessor <source-file> [dest-file] [--switch1 [value1]] [--switch2 [value2]] [...].

If dest is not given, the standard output will be assumed. It's useful if we have to pipe that into another program.

All switches are identifiers we have used in our source-file. See below.

Any alpha-numric string can be used as a switch. Just try to be consistent with other projects.

Some examples:

• smarter-preprocessor main.js main.debug.js --debug: build the main.debug.js file from main.js, using the debug parameter
• smarter-preprocessor main.js main.trace.js --loglevel trace: build the main.trace.js file from main.js, setting the loglevel parameter to 'trace'

Require a module and pre-process it on-the-fly

Smarter Preprocessor can require a module while pre-processing it on-the-fly.

module.preprocessorRequire( modulePath , switches , [ options ] )

• modulePath: string the module file path to load
• switches: object an object containing the preprocessor switches
• options: object optional, contains some options, available options are:
  • multi: if the module is required multiple times with different switches objects, multiple instances of the module will be spawned. Without this options, subsequent require will use the first instance even if the switches object has different options. Some node.js module execute code at require-time, that's why the default behaviour is to share only one instance, just like a normal require() does.

var spp = require( 'smarter-preprocessor' ) ;	// Load the smarter preprocessor module

var myModule = module.preprocessorRequire( 'my-module' , { config1: true , config2: 4 } ) ;

The .preprocessorRequire() method is added to the module prototype itself, that way, ISO behavior with vanilla require() is guaranted. Also this method is accessible from files that do not require 'smarter-preprocessor' directly.

Recommendations / Good practices

• Your source code should be working without any preprocessing. That's what make Preprocessor.js a bad thing, Javascript must run unprocessed, out of the box.
• In fact, your source code should be your standard / production version
• Use runtime module.preprocessorRequire() only for development, debugging, or any kind of fail-safe or emergency mode, that's not a good practice to use it for production running in standard mode.