Property 'type' does not exist on type 'object', even after `"type" in` check

Issue

This code fails to compile:

const nodeIsUseless = (node: unknown) =>
  node !== null &&
  typeof node === "object" &&
  "type" in node &&
  typeof node.type === "string" &&
  node.type === "JSXText";

because on the last 2 lines:

Property 'type' does not exist on type 'object'.(2339)

...which I can understand by itself, but I do not understand why after "type" in node check, TS infers node to still be of type object instead of type { type: unknown; [key: string]: unknown }, which would not trigger error.

Solution

While the code is correct, TypeScript doesn't have the capability to infer { type: unknown } from "type" in node but this feature is currently in development

Answered By - Nino Filiu