How to Code in JavaScript/TypeScript Using AI

In short: say the Node version and “no npm packages”, give one example, ask for node:test tests, run node --test.

Why JavaScript with AI

JavaScript runs websites, servers (Node.js) and apps. There are many ways to do one thing, and old examples are everywhere. A clear prompt keeps the AI on modern, simple code.

What you need

• Node.js 20 or newer: includes node --test, the built-in test runner.
• An editor + assistant: VS Code with GitHub Copilot or Claude Code, or WebStorm with Copilot.
• TypeScript (optional): npm i -D typescript and run npx tsc --noEmit to type-check.

How it flows

Install and check

1. Install Node.js LTS from nodejs.org (or nvm install --lts).
2. Check it: node -v should show v20 or newer.
3. Make a folder: mkdir slug-demo && cd slug-demo.
4. Optional: npm init -y to create package.json. Set "test": "node --test" under scripts.

Step 1 — the prompt

Step 2 — the code (tested here)

// Turn a title into a URL slug. Built with an AI assistant, then tested.
function slugify(title) {
  if (typeof title !== "string") throw new TypeError("title must be a string");
  return title
    .normalize("NFKD")
    .replace(/[\u0300-\u036f]/g, "")
    .toLowerCase()
    .replace(/[^a-z0-9]+/g, "-")
    .replace(/^-+|-+$/g, "");
}
module.exports = { slugify };
if (require.main === module) console.log(slugify(process.argv[2] || "Hello, World! 2026"));

Step 3 — run it

node slugify.js "Hello, World! 2026"
# -> hello-world-2026

Step 4 — ask for tests, then run them

const test = require("node:test");
const assert = require("node:assert");
const { slugify } = require("./slugify");

test("basic title", () => {
  assert.strictEqual(slugify("Hello, World! 2026"), "hello-world-2026");
});
test("accents and extra spaces", () => {
  assert.strictEqual(slugify("  Café   Menu  "), "cafe-menu");
});
test("rejects non-string", () => {
  assert.throws(() => slugify(42), TypeError);
});

node --test
# -> tests 3, pass 3, fail 0

TypeScript version (same idea)

Ask: “Convert slugify.js to TypeScript with strict types.” The function signature becomes:

export function slugify(title: string): string { ... }

Then run npx tsc --noEmit to check types before you run it.

Settings and config

1. Tell the AI your module style: CommonJS (require) or ES modules (import, "type": "module" in package.json). Mixing them is a common AI mistake.
2. Project rules file: add “Node 20, node:test, no new npm packages without asking” to .github/copilot-instructions.md or CLAUDE.md.
3. Lint: npm init @eslint/config@latest then npx eslint ..

Watch out (common AI mistakes in JS)

Quick quiz

Save tokens and money

Paste only the function, not node_modules or a lock file. Never let the AI read package-lock.json unless needed, it is huge. Ask for one function plus tests, then the next.

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