website: add support for JS/TS unit testing

Change-Id: I8bb35b7183c07c44c5e5da8dc2f2c15cc38ea64b
Reviewed-on: https://go-review.googlesource.com/c/website/+/377734
Run-TryBot: Jamal Carvalho <jamal@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alex Rakoczy <alex@golang.org>
Trust: Jamal Carvalho <jamalcarvalho@google.com>

.eslintrc.yaml

@@ -1,7 +1,7 @@
 root: true
 extends: google
 parserOptions:
-  ecmaVersion: 6
+  ecmaVersion: 2018
 rules:
   require-jsdoc: 'off'
   indent: 'off'

README.md

@@ -53,6 +53,13 @@ Reference .ts files in html templates as module code.
 
   `<script type="module" src="/ts/filename.ts">`
 
+Write unit tests for TypeScript code using the [jest](https://jestjs.io/)
+testing framework.
+
+### Run Jest
+
+    ./npx jest [TestPathPattern]
+
 ## Deploying
 
 Each time a CL is reviewed and submitted, the code is deployed to App Engine.

jest-transform.cjs

@@ -0,0 +1,26 @@
+/**
+ * @license
+ * Copyright 2022 The Go Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file.
+ */
+
+const {transform} = require('esbuild');
+
+exports.createTransformer = () => ({
+  canInstrument: true,
+  processAsync: async (source) => {
+    const result = await transform(source, {
+      loader: 'ts',
+    });
+    if (result.warnings.length) {
+      result.warnings.forEach(m => {
+        console.warn(m);
+      });
+    }
+    return {
+      code: result.code,
+      map: result.map,
+    };
+  },
+});

npm

@@ -7,6 +7,7 @@ docker run \
   --rm \
   --volume $(pwd):/workspace \
   --workdir /workspace \
+  --env NODE_OPTIONS="--experimental-vm-modules --no-warnings" \
   --entrypoint npm \
   node:16.13.1-alpine3.14 \
   $@

npx

@@ -7,6 +7,7 @@ docker run \
   --rm \
   --volume $(pwd):/workspace \
   --workdir /workspace \
+  --env NODE_OPTIONS="--experimental-vm-modules --no-warnings" \
   --entrypoint npx \
   node:16.13.1-alpine3.14 \
   $@

package.json

@@ -1,16 +1,28 @@
 {
   "devDependencies": {
-    "@typescript-eslint/eslint-plugin": "^5.9.0",
+    "@types/jest": "27.4.0",
+    "@typescript-eslint/eslint-plugin": "5.9.0",
     "@typescript-eslint/parser": "5.9.0",
+    "esbuild": "0.14.11",
     "eslint": "8.6.0",
     "eslint-config-google": "0.14.0",
     "eslint-config-prettier": "8.3.0",
     "eslint-plugin-prettier": "4.0.0",
+    "jest": "27.4.7",
     "prettier": "2.5.1",
     "stylelint-config-prettier": "9.0.3",
     "stylelint-config-standard": "24.0.0",
     "stylelint-order": "5.0.0",
     "stylelint-prettier": "2.0.0",
     "typescript": "4.5.4"
+  },
+  "jest": {
+    "extensionsToTreatAsEsm": [
+      ".ts"
+    ],
+    "testEnvironment": "jsdom",
+    "transform": {
+      "\\.ts$": "<rootDir>/jest-transform.cjs"
+    }
   }
 }

tsconfig.json

@@ -2,6 +2,7 @@
   "compilerOptions": {
     /* Visit https://aka.ms/tsconfig.json to read more about this file */
     "target": "es2018",
+    "module": "es2020",
     "isolatedModules": true,
     "esModuleInterop": true,
     "forceConsistentCasingInFileNames": true,