build: add JS and CSS linters

.eslintignore

@@ -0,0 +1,6 @@
+dist/
+docs/
+vendor/
+node_modules/
+*.min.js
+jquery.tools.js

.eslintrc.js

@@ -0,0 +1,12 @@
+module.exports =  {
+  env: {
+  	browser: true,
+  	jquery: true,
+  	es6: true
+  },
+  extends:  [
+    'wordpress',
+    'plugin:prettier/recommended',  // Enables eslint-plugin-prettier and displays prettier errors as ESLint errors. Make sure this is always the last configuration in the extends array.
+  ],
+  rules:  {},
+};

.gitignore

@@ -1,5 +1,6 @@
 .phpdoc/
 vendor/
+node_modules/
 dist/
 tmp/
 

.prettierrc

@@ -0,0 +1,7 @@
+{
+  "semi": true,
+  "trailingComma": "all",
+  "singleQuote": true,
+  "printWidth": 120,
+  "tabWidth": 2
+}

.stylelintignore

@@ -0,0 +1,4 @@
+dist/
+docs/
+vendor/
+node_modules/

.stylelintrc.json

@@ -0,0 +1,3 @@
+{
+  "extends": "stylelint-config-wordpress",
+}

package.json

@@ -0,0 +1,19 @@
+{
+  "scripts": {
+    "lint": "npm run lint:js && npm run lint:css",
+    "lint:fix": "npm run lint:js:fix && npm run lint:css:fix",
+    "lint:js": "eslint \"./js/*.js\"",
+    "lint:js:fix": "npm run lint:js -- --fix",
+    "lint:css": "stylelint \"./css/*.css\"",
+    "lint:css:fix": "npm run lint:css -- --fix"
+  },
+  "devDependencies": {
+    "eslint": "^7.24.0",
+    "eslint-config-prettier": "^8.2.0",
+    "eslint-config-wordpress": "^2.0.0",
+    "eslint-plugin-prettier": "^3.4.0",
+    "prettier": "^2.2.1",
+    "stylelint": "^13.12.0",
+    "stylelint-config-wordpress": "^17.0.0"
+  }
+}