Convert to TypeScript

.babelrc

@@ -1,3 +1,6 @@
 {
-  "presets": [["@babel/preset-env", { "targets": "defaults" }]]
+  "presets": [
+    ["@babel/preset-env", { "targets": "defaults" }],
+    "@babel/preset-typescript"
+  ]
 }

.eslintrc.cjs

@@ -0,0 +1,13 @@
+module.exports = {
+  extends: [
+    'eslint:recommended',
+    'plugin:@typescript-eslint/recommended-type-checked',
+  ],
+  plugins: ['@typescript-eslint'],
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    project: true,
+    tsconfigRootDir: __dirname,
+  },
+  root: true,
+};

docs/demo/demo.js

@@ -227,7 +227,6 @@
       }
     },
     getJson: function (url, callback) {
-      /* global XMLHttpRequest */
       let request = new XMLHttpRequest();
       request.open('GET', url, true);
       request.onreadystatechange = function () {
@@ -236,7 +235,6 @@
           try {
             data = JSON.parse(this.responseText, jsondiffpatch.dateReviver);
           } catch (parseError) {
-            // eslint-disable-next-line n/no-callback-literal
             return callback('parse error: ' + parseError);
           }
           if (this.status >= 200 && this.status < 400) {