Webpack 4 Config for WordPress plugin, theme, and block development

.eslintignore

**/*.min.js
**/*.build.js
**/node_modules/**
**/vendor/**
build
coverage
cypress
node_modules
vendor

eslintrc.json

{
  "root": true,
  "parser": "babel-eslint",
  "extends": [
    "wordpress",
    "plugin:react/recommended",
    "plugin:jsx-a11y/recommended",
    "plugin:jest/recommended"
  ],
  "env": {
    "browser": false,
    "es6": true,
    "node": true,
    "mocha": true,
    "jest/globals": true
  },
  "parserOptions": {
    "sourceType": "module",
    "ecmaFeatures": {
      "jsx": true
    }
  },
  "globals": {
    "wp": true,
    "wpApiSettings": true,
    "window": true,
    "document": true
  },
  "plugins": [
    "react",
    "jsx-a11y",
    "jest"
  ],
  "settings": {
    "react": {
      "pragma": "wp"
    }
  },
  "rules": {
    "array-bracket-spacing": [
      "error",
      "always"
    ],
    "brace-style": [
      "error",
      "1tbs"
    ],
    "camelcase": [
      "error",
      {
        "properties": "never"
      }
    ],
    "comma-dangle": [
      "error",
      "always-multiline"
    ],
    "comma-spacing": "error",
    "comma-style": "error",
    "computed-property-spacing": [
      "error",
      "always"
    ],
    "constructor-super": "error",
    "dot-notation": "error",
    "eol-last": "error",
    "eqeqeq": "error",
    "func-call-spacing": "error",
    "indent": [
      "error",
      "tab",
      {
        "SwitchCase": 1
      }
    ],
    "jsx-a11y/label-has-for": [
      "error",
      {
        "required": "id"
      }
    ],
    "jsx-a11y/media-has-caption": "off",
    "jsx-a11y/no-noninteractive-tabindex": "off",
    "jsx-a11y/role-has-required-aria-props": "off",
    "jsx-quotes": "error",
    "key-spacing": "error",
    "keyword-spacing": "error",
    "lines-around-comment": "off",
    "no-alert": "error",
    "no-bitwise": "error",
    "no-caller": "error",
    "no-console": "error",
    "no-const-assign": "error",
    "no-debugger": "error",
    "no-dupe-args": "error",
    "no-dupe-class-members": "error",
    "no-dupe-keys": "error",
    "no-duplicate-case": "error",
    "no-duplicate-imports": "error",
    "no-else-return": "error",
    "no-eval": "error",
    "no-extra-semi": "error",
    "no-fallthrough": "error",
    "no-lonely-if": "error",
    "no-mixed-operators": "error",
    "no-mixed-spaces-and-tabs": "error",
    "no-multiple-empty-lines": [
      "error",
      {
        "max": 1
      }
    ],
    "no-multi-spaces": "error",
    "no-multi-str": "off",
    "no-negated-in-lhs": "error",
    "no-nested-ternary": "error",
    "no-redeclare": "error",
    "no-restricted-syntax": [
      "error",
      {
        "selector": "ImportDeclaration[source.value=/^@wordpress\\u002F.+\\u002F/]",
        "message": "Path access on WordPress dependencies is not allowed."
      },
      {
        "selector": "ImportDeclaration[source.value=/^blocks$/]",
        "message": "Use @wordpress/blocks as import path instead."
      },
      {
        "selector": "ImportDeclaration[source.value=/^components$/]",
        "message": "Use @wordpress/components as import path instead."
      },
      {
        "selector": "ImportDeclaration[source.value=/^date$/]",
        "message": "Use @wordpress/date as import path instead."
      },
      {
        "selector": "ImportDeclaration[source.value=/^editor$/]",
        "message": "Use @wordpress/editor as import path instead."
      },
      {
        "selector": "ImportDeclaration[source.value=/^element$/]",
        "message": "Use @wordpress/element as import path instead."
      },
      {
        "selector": "ImportDeclaration[source.value=/^i18n$/]",
        "message": "Use @wordpress/i18n as import path instead."
      },
      {
        "selector": "ImportDeclaration[source.value=/^data$/]",
        "message": "Use @wordpress/data as import path instead."
      },
      {
        "selector": "ImportDeclaration[source.value=/^utils$/]",
        "message": "Use @wordpress/utils as import path instead."
      },
      {
        "selector": "CallExpression[callee.name=/^__|_n|_x$/]:not([arguments.0.type=/^Literal|BinaryExpression$/])",
        "message": "Translate function arguments must be string literals."
      },
      {
        "selector": "CallExpression[callee.name=/^_n|_x$/]:not([arguments.1.type=/^Literal|BinaryExpression$/])",
        "message": "Translate function arguments must be string literals."
      },
      {
        "selector": "CallExpression[callee.name=_nx]:not([arguments.2.type=/^Literal|BinaryExpression$/])",
        "message": "Translate function arguments must be string literals."
      }
    ],
    "no-shadow": "error",
    "no-undef": "error",
    "no-undef-init": "error",
    "no-unreachable": "error",
    "no-unsafe-negation": "error",
    "no-unused-expressions": "error",
    "no-unused-vars": "error",
    "no-useless-computed-key": "error",
    "no-useless-constructor": "error",
    "no-useless-return": "error",
    "no-var": "error",
    "no-whitespace-before-property": "error",
    "object-curly-spacing": [
      "error",
      "always"
    ],
    "prefer-const": "error",
    "quote-props": [
      "error",
      "as-needed"
    ],
    "react/display-name": "off",
    "react/jsx-curly-spacing": [
      "error",
      {
        "when": "never",
        "children": true
      }
    ],
    "react/jsx-equals-spacing": "error",
    "react/jsx-indent": [
      "error",
      "tab"
    ],
    "react/jsx-indent-props": [
      "error",
      "tab"
    ],
    "react/jsx-key": "error",
    "react/jsx-tag-spacing": "error",
    "react/no-children-prop": "off",
    "react/no-find-dom-node": "warn",
    "react/prop-types": "off",
    "semi": "error",
    "semi-spacing": "error",
    "space-before-blocks": [
      "error",
      "always"
    ],
    "space-before-function-paren": [
      "error",
      "never"
    ],
    "space-in-parens": [
      "error",
      "always"
    ],
    "space-infix-ops": [
      "error",
      {
        "int32Hint": false
      }
    ],
    "space-unary-ops": [
      "error"
    ],
    "template-curly-spacing": [
      "error",
      "always"
    ],
    "valid-jsdoc": [
      "error",
      {
        "requireReturn": false
      }
    ],
    "valid-typeof": "error",
    "yoda": "off"
  }
}

package.json

{
	"name": "my-thing",
	"description": "A description of my thing.",
	"author": "Micah Wood <micah@wpscholar.com> (http://wpscholar.com)",
	"license": "proprietary",
	"private": true,
	"scripts": {
		"build": "cross-env NODE_ENV=production webpack",
		"lint": "eslint build/js/**/*",
		"start": "webpack --watch",
		"test": "echo \"Error: no test specified\" && exit 1"
	},
	"dependencies": {
		"classnames": "^2.2.5"
	},
	"devDependencies": {
    		"@babel/core": "^7.1.2",
	    	"@wordpress/babel-plugin-makepot": "^2.1.1",
	    	"@wordpress/babel-preset-default": "^3.0.0",
    		"@wordpress/browserslist-config": "^2.1.3",
	    	"@wordpress/i18n": "^3.0.0",
    		"ajv": "^6.5.4",
	    	"autoprefixer": "^9.1.5",
    		"babel-eslint": "^10.0.1",
	    	"babel-loader": "^8.0.4",
    		"babel-plugin-transform-class-properties": "^6.24.1",
	    	"cross-env": "^5.0.1",
    		"css-loader": "^1.0.0",
	    	"eslint": "^5.6.1",
    		"eslint-config-wordpress": "^2.0.0",
	    	"eslint-plugin-jest": "^21.6.1",
    		"eslint-plugin-jsx-a11y": "^6.0.3",
	    	"eslint-plugin-react": "^7.5.1",
    		"eslint-plugin-wordpress": "^0.1.0",
	    	"file-loader": "^2.0.0",
    		"import-glob": "^1.5.0",
	    	"mini-css-extract-plugin": "^0.4.0",
    		"node-sass": "^4.9.0",
	    	"node-sass-glob-importer": "^5.1.2",
    		"postcss-loader": "^3.0.0",
	    	"raw-loader": "^0.5.1",
    		"sass-loader": "^7.0.1",
	    	"style-loader": "^0.23.0",
    		"webpack": "^4.20.2",
	    	"webpack-cli": "^3.1.1"
	}
}

webpack.config.js

'use strict';

const autoprefixer = require( 'autoprefixer' );
const fs = require( 'fs' );
const globImporter = require( 'node-sass-glob-importer' );
const browsers = require( '@wordpress/browserslist-config' );
const MiniCssExtractPlugin = require( 'mini-css-extract-plugin' );
const path = require( 'path' );
const webpack = require( 'webpack' );

module.exports = function() {

	const mode = process.env.NODE_ENV || 'development';
	const extensionPrefix = mode === 'production' ? '.min' : '';

	// This is the URL path relative to the root domain.
	const publicPath = '/wp-content/mu-plugins/blocks/';

	// These are the paths where different types of resources should end up.
	const paths = {
		css: 'assets/css/',
		img: 'assets/img/',
		font: 'assets/font/',
		js: 'assets/js/',
		lang: 'languages/',
	};

	// The property names will be the file names, the values are the files that should be included.
	const entry = {
		blocks: [
			'./build/scss/blocks.scss',
		],
		editor: [
			'./build/js/editor.js',
			'./build/scss/editor.scss',
		],
	};

	const loaders = {
		css: {
			loader: 'css-loader',
			options: {
				sourceMap: true,
			},
		},
		postCss: {
			loader: 'postcss-loader',
			options: {
				plugins: [
					autoprefixer( {
						browsers,
						flexbox: 'no-2009',
					} ),
				],
				sourceMap: true,
			},
		},
		sass: {
			loader: 'sass-loader',
			options: {
				importer: globImporter(),
				sourceMap: true,
			},
		},
	};

	const config = {
		mode,
		entry,
		output: {
			path: path.join( __dirname, '/' ),
			publicPath,
			filename: `${ paths.js }[name]${ extensionPrefix }.js`,
		},
		externals: {
			'@wordpress/a11y': 'wp.a11y',
			'@wordpress/components': 'wp.components', // Not really a package.
			'@wordpress/blocks': 'wp.blocks', // Not really a package.
			'@wordpress/data': 'wp.data', // Not really a package.
			'@wordpress/date': 'wp.date', // Not really a package.
			'@wordpress/element': 'wp.element', // Not really a package.
			'@wordpress/hooks': 'wp.hooks',
			'@wordpress/i18n': 'wp.i18n',
			'@wordpress/utils': 'wp.utils', // Not really a package
			backbone: 'Backbone',
			jquery: 'jQuery',
			lodash: 'lodash',
			moment: 'moment',
			react: 'React',
			'react-dom': 'ReactDOM',
			tinymce: 'tinymce',
		},
		module: {
			rules: [
				{
					enforce: 'pre',
					test: /\.js|.jsx/,
					loader: 'import-glob',
					exclude: /(node_modules)/,
				},
				{
					test: /\.js|.jsx/,
					loader: 'babel-loader',
					query: {
						presets: [
							'@wordpress/default',
						],
						plugins: [
							[
								'@wordpress/babel-plugin-makepot',
								{
									'output': `${ paths.lang }translation.pot`,
								}
							],
							'transform-class-properties',
						],
					},
					exclude: /(node_modules|bower_components)/,
				},
				{
					test: /\.html$/,
					loader: 'raw-loader',
					exclude: /node_modules/,
				},
				{
					test: /\.css$/,
					use: [
						MiniCssExtractPlugin.loader,
						loaders.css,
						loaders.postCss,
					],
					exclude: /node_modules/,
				},
				{
					test: /\.scss$/,
					use: [
						MiniCssExtractPlugin.loader,
						loaders.css,
						loaders.postCss,
						loaders.sass,
					],
					exclude: /node_modules/,
				},
				{
					test: /\.(ttf|eot|svg|woff2?)(\?v=[0-9]\.[0-9]\.[0-9])?$/,
					use: [
						{
							loader: 'file-loader',
							options: {
								name: '[name].[ext]',
								outputPath: paths.font,
							},
						},
					],
					exclude: /(assets)/,
				},
			],
		},
		plugins: [
			new MiniCssExtractPlugin( {
				filename: `${ paths.css }[name]${ extensionPrefix }.css`,
			} ),
			new webpack.DefinePlugin( {
				'process.env.NODE_ENV': JSON.stringify( mode ),
			} ),
			function() {
				// Custom webpack plugin - remove generated JS files that aren't needed
				this.hooks.done.tap( 'webpack', function( stats ) {
					stats.compilation.chunks.forEach( chunk => {
						if ( ! chunk.entryModule._identifier.includes( '.js' ) ) {
							chunk.files.forEach( file => {
								if ( file.includes( '.js' ) ) {
									fs.unlinkSync( path.join( __dirname, `/${ file }` ) );
								}
							} );
						}
					} );
				} );
			},
		],
	};

	if ( mode !== 'production' ) {
		config.devtool = 'source-map';
	}

	return config;
};

@jackjwilliams A new file will be created for each entry point. You can have as many entry points as you want. See https://gist.github.com/wpscholar/261141cf7b2bf4efd45cb86ad0a43ff2#file-webpack-config-js-L29