Move to es6

.eslintrc

@@ -1,9 +1,6 @@
 {
-  "extends": ["airbnb-base/legacy", "prettier"],
+  "extends": ["airbnb-base", "prettier"],
   "env": {
     "node": true
-  },
-  "rules": {
-    "func-names": 0
   }
 }

lib/index.js

@@ -1,24 +1,22 @@
-var _ = require('lodash');
-var stylelint = require('stylelint');
-var doiuse = require('doiuse');
-var Result = require('postcss/lib/result');
+const _ = require('lodash');
+const stylelint = require('stylelint');
+const doiuse = require('doiuse');
+const Result = require('postcss/lib/result');
 
 /**
  * Plugin settings
  */
 
-var ruleName = 'plugin/no-unsupported-browser-features';
-var messages = stylelint.utils.ruleMessages(ruleName, {
-  rejected: function rejectRule(details) {
-    return 'Unexpected browser feature ' + details;
-  }
+const ruleName = 'plugin/no-unsupported-browser-features';
+const messages = stylelint.utils.ruleMessages(ruleName, {
+  rejected: details => `Unexpected browser feature ${details}`
 });
 
 /**
  * Options
  */
 
-var optionsSchema = {
+const optionsSchema = {
   browsers: [_.isString],
   ignore: [_.isString]
 };
@@ -29,21 +27,21 @@ var optionsSchema = {
 
 function cleanWarningText(warningText) {
   // Get index of feature Id
-  var featureIdIndex = warningText.lastIndexOf('(');
+  const featureIdIndex = warningText.lastIndexOf('(');
 
   // Get feature Id, then replace brackets with quotes
-  var featureId = warningText.slice(featureIdIndex, warningText.length).replace(/\(|\)/g, '"');
+  const featureId = warningText.slice(featureIdIndex, warningText.length).replace(/\(|\)/g, '"');
 
   // Get start of support text i.e. "x not supported by...", or "y only partially supported by..."
-  var browserSupportStartIndex =
+  const browserSupportStartIndex =
     warningText.indexOf('not') !== -1 ? warningText.indexOf('not') : warningText.indexOf('only');
 
   // Get browser support text, then strip brackets.
-  var browserSupport = warningText
+  const browserSupport = warningText
     .slice(browserSupportStartIndex, featureIdIndex - 1)
     .replace(/\(|\)|:/g, '');
 
-  var cleanedWarningText = featureId + ' is ' + browserSupport;
+  const cleanedWarningText = `${featureId} is ${browserSupport}`;
 
   return cleanedWarningText;
 }
@@ -53,23 +51,23 @@ function cleanWarningText(warningText) {
  */
 
 function ruleFunction(on, options) {
-  return function postCssPlugin(root, result) {
-    var validOptions = stylelint.utils.validateOptions(result, ruleName, {
+  return (root, result) => {
+    const validOptions = stylelint.utils.validateOptions(result, ruleName, {
       actual: options,
       possible: optionsSchema,
       optional: true
     });
 
-    var doiuseOptions = _.pick(options, Object.keys(optionsSchema));
-    var doiuseResult = new Result();
+    const doiuseOptions = _.pick(options, Object.keys(optionsSchema));
+    const doiuseResult = new Result();
 
     if (!validOptions) return;
 
     doiuse(doiuseOptions).postcss(root, doiuseResult);
-    doiuseResult.warnings().forEach(function reportWarning(doiuseWarning) {
+    doiuseResult.warnings().forEach(doiuseWarning => {
       stylelint.utils.report({
-        ruleName: ruleName,
-        result: result,
+        ruleName,
+        result,
         message: messages.rejected(cleanWarningText(doiuseWarning.text)),
         node: doiuseWarning.node,
         line: doiuseWarning.line,