Versions

Compare two TypeScript versions on the same type

One snippet, two TypeScript releases, two compilers running side by side in your browser. Three things can differ and all three are things a release note either does not mention or does not state precisely: the type your code resolves to, the diagnostics it raises, and what it cost to check. Nothing else is reported.

The pair spans the 5.x feature run. It answers whether a type works on an older compiler — not what changed in any particular minor release.

Scratch

scratch.ts

// The same snippet, run through both compilers.
// What differs is marked; what matches is left alone.

type Rename<T> = { [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K] }

type Api = Rename<{ id: number; name: string }>

// NoInfer arrived in TypeScript 5.4. Before that it is a missing name.
type Clamp = NoInfer<string> | number

// The same snippet, run through both compilers.
// What differs is marked; what matches is left alone.

type Rename<T> = { [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K] }

type Api = Rename<{ id: number; name: string }>

// NoInfer arrived in TypeScript 5.4. Before that it is a missing name.
type Clamp = NoInfer<string> | number

Each compiler is a separate download, fetched the first time you compare.

Not compared yet.