add eslint

.eslintrc.cjs

@@ -0,0 +1,27 @@
+/* eslint-env node */
+module.exports = {
+  ignorePatterns: ["/target/**", "/jest.config.js"],
+  extends: ["eslint:recommended", "plugin:@typescript-eslint/recommended"],
+  parser: "@typescript-eslint/parser",
+  plugins: ["@typescript-eslint"],
+  root: true,
+  rules: {
+    // Sometimes you just need a `while(true)`.
+    "no-constant-condition": "off",
+    // Typescript already checks problematic fallthrough.
+    // The eslint rule is a bit dumb and also complains about
+    // obvious clear fallthrough like `case "a": case "b"`.
+    "no-fallthrough": "off",
+    // Suppress no-unused-vars with leading underscores.
+    "@typescript-eslint/no-unused-vars": [
+      "warn",
+      {
+        varsIgnorePattern: "^_",
+        argsIgnorePattern: "^_",
+      },
+    ],
+    // `any` is genrally bad, but sometimes it's the nicest solution
+    // Just let me use it without any ceremony.
+    "@typescript-eslint/no-explicit-any": "off",
+  },
+};