Peterbe.com

My colleague @mattcosta7 demonstrated something that feels obvious in hindsight.

Instead of enums, use a regular object. So instead of

enum State {
  SOLID,
  LIQUID,
  GAS,
}

(playground here - note how "complex" the transpiled JavaScript becomes)

...use an object. Objects have the advantage that when the TypeScript is converted to JavaScript, it looks pretty much identical. TypeScript 5.8 makes it possible to disallow "non-erasable syntax" which means you can set up your tsconfig.json to avoid enum.

The alternative is an object. It's a bit more verbose but it has advantages:

const State = {
  SOLID: "solid",
  LIQUID: "liquid",
  GAS: "gas"
} as const

type State = typeof State[keyof typeof State]

(playground here - note how simple the transpiled JavaScript is)

In the above code, if you hover the mouse over State it'll say

'solid' | 'liquid' | 'gas'

A couple of months ago I wrote about "Node watch mode and TypeScript" which suggests using the @swc-node/register package to be able to run node on .ts file without first converting it to .js using tsc.

In Node 22, you don't even need @swc-node/register. You can use --experimental-strip-types instead. (Note the prefix "experimental"). See release notes here.

Imagine a script like this:

// example.ts

function c2f(c: number) {
  return (c * 9) / 5 + 32;
}
console.log(c2f(123));

you can execute it directly in Node v22 using:

❯ node --experimental-strip-types --no-warnings example.ts
253.4

I'm writing this blog post from an admin interface I built, which is a web app frontend for the backend behind peterbe.com. It's built as a single-page app in Vite, with React.
Vite, unlike frameworks like Remix or Next, doesn't come with its own routing. You have to add that yourself. I added React Router. Another thing you have to do yourself is a way to load remote data into the app for display and for manipulation. This is done as XHR requests happen on the client side. For that, I chose TanStack Query. If you haven't used it but used React, it's sugar for this type of code:

// DON'T DO THIS. USE TANSTACK QUERY

const [stuff, setStuff] = useState(null)
const [error, setError] = useState(null)
useEffect(() => {
  fetch('/api/some/thing')
    .then(r => r.json())
    .then(data => setStuff(data)
    .catch(err => setError(err))
}, [])

This one always confused me but by blogging about it, hopefully, it will stick.

This does NOT work in TypeScript:

const person = {
  firstName: "peter",
  lastName: "bengtsson",
  state: "happy"
}

const keys = Object.keys(person)
const randomKey = keys[Math.floor(Math.random() * keys.length)];
const value = person[randomKey]

It works in JavaScript, but in TypeScript you get an error on the last line (from the person[randomKey]):

I have a web app that operates as a SPA (Single Page App). It's built on regular Vite + React + TypeScript. In production you just host the built static assets, but in development (for hot module reloading and stuff) I use the built-in dev server in Vite. This is what you get when you type vite without any other command line arguments.

But here's what happens, you're in the terminal and you type npm run dev and hit Enter. Then, using your trackpad or keyboard shortcuts you switch over to a browser tab and go to http://localhost:5173/. When you get there to the first request, Vite starts at the entry point, which is src/main.tsx and from there, it looks at its imports and starts transpiling the files needed. You can see what happens with vite --debug transform.

With debug:

Suppose you have a function, written in TypeScript, that is fine and complete. Now you want to write a function that works like that one but with just some slightly more parameters and other differences. It's not too different from a decorator function.

Extending the list of parameters

Let's imagine that you already have this function:

type Operation = "sum" | "sub" | "mul" | "div"

function calculator(a: number, b: number, op: Operation) {
  if (op === "sum") return a + b
  if (op === "sub") return a - b
  if (op === "mul") return a * b
  if (op === "div") return a / b
  throw new Error(op)
}

And this could, for the sake of argument, be in a different file and/or possibly outside your control. What you now want to do is write a new function that takes those same arguments, plus one more. And importantly, you don't want to have to spell out all the arguments one more time.

First, the WRONG way to solve this:

import { calculator } from './calculator' // The code in the snippet above

type Operation = "sum" | "sub" | "mul" | "div"

function doubleCalculator(a: number, b: number, op: Operation, c: number) {
  return calculator(calculator(a, b, op), c, op)
}

console.log(calculator(1, 2, "sum")) // 3
console.log(doubleCalculator(1, 2, "sum", 10)) // 13

Technically, it works, but you had to repeat the calculator function's signature.

Bun 1.1.30 came out last week. What got me intrigued is this new option to bun build which is --bytecode. With it you can create an executable, supposedly compiled partially to bytecode which means it can start even faster.

I tried it on my hylite CLI which is a CLI, built with Bun, but works in all versions of Node, that can syntax highlight code to HTML on the command line. Here's what I did:

What @tanstack/react-query is is a fancy way of fetching data, on the client, in a React app.

Simplified primer by example; instead of...

function MyComponent() {
  const [userInfo, setUserInfo] = useState(null)
  useEffect(() => {
    fetch('/api/user/info')
    .then(response => response.json())
    .then(data => {
      setUserInfo(data)
    })
  }, [])

  return <div>Username: {userInfo ? userInfo.user_name : <em>not yet known</em>}</div>
}

I have a single-page-app built with React and Vite. It fetches data entirely on the client-side after it has started up. So there's no server at play other than the server that hosts the static assets.
Until yesterday, the app was use swr to fetch data, now it's using @tanstack/react-query instead. Why? Because I'm curious. This blog post attempts to jot down some of the difference and contrasts.

If you want to jump straight to the port diff, look at this commit: https://github.com/peterbe/analytics-peterbecom/pull/47/commits/eac4f873303bfb493320b0b4aa0f5f6ba133001a

Bundle phobia

When @tanstack/react-query first came out, back in the day when it was called React Query, I looked into it and immediately got scared how large it was. I think they've done some great work to remedy that because it's now not much larger than swr. Perhaps it's because swr, since wayback when, has grown too.

When I run npm run build it spits this out:

Did you know you can attach a key to a JavaScript object that is actually a callable?

For example:

const data = await response.json()

Object.defineProperty(data, 'magic', {
  get: () => {
    return Math.random()
  },
})

console.log({magic: data.magic})

will print:

{ magic: 0.6778944803790492 }