Plugin.js

const ChainedMap = require('./ChainedMap');
const Orderable = require('./Orderable');

module.exports = Orderable(
  class extends ChainedMap {
    constructor(parent, name, type = 'plugin') {
      super(parent);
      this.name = name;
      this.type = type;
      this.extend(['init']);

      this.init((Plugin, args = []) => {
        if (typeof Plugin === 'function') {
          return new Plugin(...args);
        }
        return Plugin;
      });
    }

    use(plugin, args = []) {
      return this.set('plugin', plugin).set('args', args);
    }

    tap(f) {
      this.set('args', f(this.get('args') || []));
      return this;
    }

    merge(obj, omit = []) {
      if ('plugin' in obj) {
        this.set('plugin', obj.plugin);
      }

      if ('args' in obj) {
        this.set('args', obj.args);
      }

      return super.merge(obj, [...omit, 'args', 'plugin']);
    }

    toConfig() {
      const init = this.get('init');
      let plugin = this.get('plugin');
      const args = this.get('args');
      let pluginPath = null;

      // Support using the path to a plugin rather than the plugin itself,
      // allowing expensive require()s to be skipped in cases where the plugin
      // or webpack configuration won't end up being used.
      if (typeof plugin === 'string') {
        pluginPath = plugin;
        // eslint-disable-next-line global-require, import/no-dynamic-require
        plugin = require(pluginPath);
      }

      const constructorName = plugin.__expression
        ? `(${plugin.__expression})`
        : plugin.name;

      const config = init(plugin, args);

      Object.defineProperties(config, {
        __pluginName: { value: this.name },
        __pluginType: { value: this.type },
        __pluginArgs: { value: args },
        __pluginConstructorName: { value: constructorName },
        __pluginPath: { value: pluginPath },
      });

      return config;
    }
  },
);