Update for modern browsers

- adopt babel-preset-github (drop IE 11)
- stop transforming custom element classes
- check files with Flow

Author: mislav

.babelrc

@@ -1,22 +1,13 @@
 {
   "env": {
     "esm": {
-      "plugins": [
-        "@babel/plugin-proposal-object-rest-spread",
-        "transform-custom-element-classes"
-      ],
-      "presets": [
-        ["@babel/flow"],
-        ["@babel/env", {"modules": false}],
-      ]
+      "presets": ["github"]
     },
     "umd": {
       "plugins": [
-        "@babel/plugin-proposal-object-rest-spread",
-        "transform-custom-element-classes",
         "@babel/plugin-transform-modules-umd"
       ],
-      "presets": ["@babel/flow", "@babel/env"]
+      "presets": ["github"]
     }
   }
 }

.eslintrc.json

@@ -1,7 +1,23 @@
 {
   "extends": [
-    "plugin:github/es6",
     "plugin:github/browser",
+    "plugin:github/es6",
     "plugin:github/flow"
+  ],
+  "parser": "babel-eslint",
+  "overrides": [
+    {
+      "files": "test/**/*.js",
+      "rules": {
+        "flowtype/require-valid-file-annotation": "off",
+        "github/unescaped-html-literal": "off"
+      }
+    },
+    {
+      "files": "prettier.config.js",
+      "rules": {
+        "flowtype/require-valid-file-annotation": "off"
+      }
+    }
   ]
 }

index.js

@@ -1,4 +1,4 @@
-/* @flow */
+/* @flow strict */
 
 function keydown(fn: KeyboardEventHandler): KeyboardEventHandler {
   return function(event: KeyboardEvent) {
@@ -248,14 +248,16 @@ function repeat(string: string, n: number): string {
   return Array(n + 1).join(string)
 }
 
-function wordSelectionStart(text: string, index: number): number {
+function wordSelectionStart(text: string, i: number): number {
+  let index = i
   while (text[index] && text[index - 1] != null && !text[index - 1].match(/\s/)) {
     index--
   }
   return index
 }
 
-function wordSelectionEnd(text: string, index: number): number {
+function wordSelectionEnd(text: string, i: number): number {
+  let index = i
   while (text[index] && !text[index].match(/\s/)) {
     index++
   }