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commonjs-modules-javax-script

A simple implementation of require() for use in Java's embedded Javascript engine (JRE 6,7 and 8)

Goal

To provide a require() function which supports CommonJS style modules in the Javascript engine bundled with Java 6, 7 and 8. This is not meant to be a full port of commonjs or node modules, this is just the require() function.

require - CommonJS-style module loading in Java 6,7 and 8's Javascript Engine.

Node.js is a server-side javascript environment with an excellent module loading system based on CommonJS. Modules in Node.js are really simple. Each module is in its own javascript file and all variables and functions within the file are private to that file/module only. There is a very concise explanation of CommonJS modules at...

http://wiki.commonjs.org/wiki/Modules/1.1.1.

Node.js also has good documentation on [Modules][njsmod].

If you want to export a variable or function you use the module.export property.

For example imagine you have 3 files program.js, inc.js and math.js ...

math.js

exports.add = function(a,b){
    return a + b;
}

inc.js

var math = require('./math');
exports.increment = function(n){
    return math.add(n, 1);
}

program.js

var inc = require('./inc').increment;
var a = 7;
a = inc(a);
print(a);

You can see from the above sample code that programs can use modules and modules themeselves can use other modules. Modules have full control over what functions and properties they want to provide to others.

Bootstrapping

To create the require function you must first load and evaluate the require.js source file. Since you can't require('require') use the native (or custom) load() function instead to first load require.js.

  • On JDK 8's Javascript Engine (Nashorn) there is a native load() function which can be used...
var Require = load('./require.js');
var require = Require( './' , [ 'libpath1', 'libpath2' ] );
// now you can use require to load commonjs/node style modules
var myModule = require('./mymodule');
  • On JDK 6 and 7 there is no native load() function so define one like this...
var load = function( path ) { 
  var line = null,
      reader = null
      contents = '';
  reader = new java.io.BufferedReader( new java.io.FileReader( new java.io.File( path ) ) );
  while ( ( line = reader.readLine() ) != null ) {
      contents += line + '\n'
  }
  return eval( '(' + contents + ')' );
}

..then bootstrap require like this...

var Require = load('./require.js');
var require = Require( new java.io.File( './' ), [ 'libpath1', 'libpath2' ] );
// now you can use require to load commonjs/node style modules
var myModule = require('./mymodule');

module name resolution

When resolving module names to file paths, use the following rules...

  1. if the module does not begin with './' or '/' then ...

    1.1 Look in any of the supplied library paths. If it's not there then throw an error.

  2. If the module begins with './' or '/' then ...

    2.1 if the module begins with './' then it's treated as a file path. File paths are always relative to the module from which the require() call is being made.

    2.2 If the module begins with '/' then it's treated as an absolute path.

    If the module does not have a '.js' suffix, and a file with the same name and a .js sufix exists, then the file will be loaded.

  3. If the module name resolves to a directory then...

    3.1 look for a package.json file in the directory and load the main property e.g.

    // package.json located in './some-library/'
    {
      "main": './some-lib.js',
      "name": 'some-library'
    }
    

    3.2 if no package.json file exists then look for an index.js file in the directory

Caveats

  • This is not battle-hardened code.
  • I don't know what I'm doing.

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A simple implementation of require() for use in Java's embedded Javascript engines (JRE 6,7,8)

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