parallel-webpack/src/loadConfigurationFile.js

var jsVars = require('interpret').jsVariants,
    endsWith = require('lodash.endswith'),
    availableExts = Object.keys(jsVars),
    chalk = require('chalk');

// sort extensions to ensure that .babel.js and
// similar ones are always matched before .js
availableExts.sort(function(a, b) {
    var res = -(a.split(/\./).length - b.split(/\./).length);
    // all things being equal, we need to
    // prioritize .js as it is most likely
    if(res === 0) {
        if(a === '.js') {
            return -1;
        }
        if(b === '.js') {
            return 1;
        }
        return 0;
    }
    return res;
});

function getMatchingLoaderFn(configPath, extensions, variants) {
    let availableExtensions =  extensions || availableExts;
    let jsVariants = variants || jsVars;
    for(var i = 0, len = availableExtensions.length; i < len; i++) {
        var ext = availableExtensions[i];
        if(endsWith(configPath, ext)) {
            return jsVariants[ext];
        }
    }
    return null;
}

function callConfigFunction(fn) {
    return fn(require('minimist')(process.argv, { '--': true }).env || {});
}

function getConfig(configPath) {
    var configModule = require(configPath);
    var configDefault = configModule && configModule.__esModule ? configModule.default : configModule;
    return typeof configDefault === 'function' ? callConfigFunction(configDefault) : configDefault;
}

module.exports = {
    default: function(configPath, matchingLoader) {
        let getMatchingLoader = matchingLoader || getMatchingLoaderFn;

        var mod = getMatchingLoader(configPath);
        if(mod) {
            var mods = Array.isArray(mod) ? mod : [mod],
                installed = false;

            for(var i = 0, len = mods.length; i < len; i++) {
                mod = mods[i];
                if(typeof mod === 'string') {
                    try {
                        require(mod);
                        installed = true;
                    } catch(ignored) {}
                } else if(typeof mod === 'object') {
                    try {
                        var s = require(mod.module);
                        mod.register(s);
                        installed = true;
                    } catch(ignored) {}
                }

                if(installed) {
                    break;
                }
            }

            if(!installed) {
                throw new Error('Could not load required module loading for ' + chalk.underline(configPath));
            }
        }
        return getConfig(configPath);
    },
    getMatchingLoader: getMatchingLoaderFn,
    availableExtensions: availableExts,
};