It's JavaScript that's complicated, not TypeScript

When I first started writing TypeScript, it felt strange and bureaucratic, like I was being asked to constantly justify things that were already obvious.

Then, after enough time, you realise TypeScript isn’t being pedantic. It’s compensating for the fact that JavaScript itself is wildly permissive.

Everything is an object, somehow

JavaScript’s type system has the energy of a witness being cross-examined.

Is this thing an object? "Yup"

An array? "Maybe"

Is it something, at least? "Probably, but it could be null"

Wait, is it a date? "Ah, you got me! Yeah, it's a date, lol…"

typeof {}          // "object"
typeof []          // "object"
typeof null        // "object"
typeof new Date()  // "object"

Which leads to half of modern frontend engineering becoming:

if (
  value &&
  typeof value === "object" &&
  !Array.isArray(value) &&
  !(value instanceof Date)
) {
  // finally, maybe (not), a plain object
}

Trust, but verify

JavaScript:

Everything is an object until proven otherwise.

TypeScript:

I would like to see the proof.

Where does it end?

There’s a comical number of things that satisfy the "object" type, including:

Arrays
null
Date
Map
Set
RegExp
Errors
Typed arrays (Uint8Array, etc.)
Promise
Boxed primitives (new String("x"))
Class instances
DOM nodes
URL
ArrayBuffer
WeakMap / WeakSet
Literally objects with custom prototypes
Objects created with Object.create(null) that aren’t even instances of Object

So, if you don't want a type guard that starts to look like:

value &&
typeof value === "object" &&
!Array.isArray(value) &&
!(value instanceof Date) &&
!(value instanceof Map) &&
!(value instanceof Set)

Just use this, which contains the accumulated trauma of an entire ecosystem:

isPlainObject(value)

jossmac/js-vs-ts.md

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