Flow now uses webpack plugins to make the webpack.generated.js cleaner and easier to extend without cluttering the file and making it long and complex.

The files get installed with the task TaskInstallFrontendBuildPlugins which reads the plugins.json in from src/main/resources/plugins and installs the plugins named here e.g.

{
  "plugins": [
    "stats-plugin"
  ]
}

The plugin itself should also be contained in src/main/resources/plugins with the folder name being the same as the plugin name.

For stats-plugin this means it should be located in src/main/resources/plugins/stats-plugin.

The plugin folder needs to contain the plugin javascript files plus a package.json with at least the fields version, main, files filled where:

• version is the semver version for the plugin. (Plugin will not be updated if the same version already exists)
• main depicts the main js file for the plugin.
• files contains all files the plugin needs. (only these files will be copied)

The full information would be preferred:

{
  "description": "stats-plugin",
  "keywords": [
    "plugin"
  ],
  "repository": "vaadin/flow",
  "name": "@vaadin/stats-plugin",
  "version": "1.0.0",
  "main": "stats-plugin.js",
  "author": "Vaadin Ltd",
  "license": "Apache-2.0",
  "bugs": {
    "url": "https://github.com/vaadin/flow/issues"
  },
  "files": [
    "stats-plugin.js"
  ]
}

For creating a plugin see Writing a plugin

Testing a plugin is often easier by using it in a project. As by default all plugins are re-copied from the flow-server.jar making changes would mean building the server module each time.

The plugins are copied to target/plugins from there they are "installed" to node_modules with (p)npm. To make editing and testing easier one can add "update": false, to the plugin package json that will make it not be overwritten.

The flow plugins get installed to node_modules/@vaadin which means that using them we should use the for @vaadin/${plugin-name}

As the plugins are meant for internal use the are added to webpack.generated.js and used from there.

First we need to import the webpack plugin

const StatsPlugin = require('@vaadin/stats-plugin');

then add the plugin with required options to plugins in the generated file

  plugins: [
    new StatsPlugin({
      devMode: devMode,
      statsFile: statsFile,
      setResults: function (statsFile) {
        stats = statsFile;
      }
    }),
 ]

To set logging for the plugins one can add to the webpack.config.js file:

  {
    stats: {
      logging: 'log'
    }
  }

where the accepted logging levels are:

• 'none', false - disable logging
• 'error' - errors only
• 'warn' - errors and warnings only
• 'info' - errors, warnings, and info messages
• 'log', true - errors, warnings, info messages, log messages, groups, clears. Collapsed groups are displayed in a collapsed state.
• 'verbose' - log everything except debug and trace. Collapsed groups are displayed in expanded state.

For debug level logs one should have the settings as:

  {
    stats: {
      logging: 'log',
      loggingDebug: [
        'theme-loader',
        'ApplicationThemePlugin',
        'FlowIdPlugin'
      ]
    }
  }