Parable - Parallel Babel Runner

This is a module that makes use of Node's cluster module to run Babel transpilation in parallel. In addition it provides the ability to cache results on disk to speed up subsequent rebuilds.

This module, and it's documentation, is still under active development and will be likely be changing often.

Current implementations for other build related tools using Parable are:

• gulp-parable
• karma-parable-preprocessor

Get in touch if you add one we can add to the list!

Usage

Basic usage as a module

const parable = require('parable');

parable.transformFiles(glob.sync('**/*.js'), {})
    .then(files => {
        console.log(files);
    });

Options

Default options:

{
    babelOptions: {},
    logLevel: 'error',
    scale: SCALE,
    processes: null,
    output: Output.STRING,
    outputDir: null,
    base: '',
    key: ''
}

babelOptions

The options to pass to the Babel transpiler (note that .babelrc files will also be read as normal). These are mostly passed as-is to Babel, so refer to Babel's options for documentation, with one exception - the two options that are a function - getModuleId and shouldPrintComment.

Since we pass options to the workers from the master using stringified JSON we can't pass a function, instead these options should be passed as a string which is the name of a module to require which will provide a function to be called. For example:

parable.transformFiles(glob.sync('**/*.js'), {
    babelOptions: {
        getModuleId: path.resolve('./babel-get-module-id')
    }
});

// babel-get-module-id.js
module.exports = (moduleName) => moduleName.toUpperCase(); // OK?!

logLevel

Level of logging to use - one of the usual suspects, error, warn, info, debug.

scale

Scale factor to apply to number of CPUs to determine how many parallel processes to run - default is 0.5 (ie. 4 processes for 8 cores). See also processes if you want to set an explicit number of processes.

processes

Number of parallel processes to run - default is number of cores / scale.

output

By default the workers will return the transpiled code, set this to parable.Output.FILE to write to a file instead. If you want to take advantage of caching between runs you will need to write to a file.

outputDir

The directory to write files to when the output is parable.Output.FILE. Defaults to a system temporary directory created using the tmp module.

base

The base directory to pass into Babel. This is used to calculate relative filenames, for example when naming AMD modules using Babel's moduleIds option.

This can be specified as a single string, or an array of base paths - if an array is supplied then the closest matching base path for the path being transpiled will be chosen. If no match is found, the path will be relative to the first entry in the base array.

key

Default is an empty string. A key for this config. As the config object is used when generating the hash, this is to ensure unique hashes if the only config differences are in .babelrc files.