add linting, do more type hinting

.eslintrc.cjs

@@ -0,0 +1,17 @@
+module.exports = {
+  root: true,
+  parser: '@typescript-eslint/parser',
+  plugins: [
+    '@typescript-eslint',
+  ],
+  parserOptions: {
+    ecmaVersion: 2020,
+  },
+  extends: [
+    'eslint:recommended',
+    'plugin:@typescript-eslint/recommended',
+  ],
+  rules: {
+    '@typescript-eslint/no-inferrable-types': 'off'
+  }
+};