Stupid Typescript tricks

tricks.ts

//// Exact types
type Exact<TExpected, TActual extends TExpected> = TExpected extends TActual ? TExpected: never;

type Foo = { x: number };
function acceptT<T extends Foo>(input: Exact<Foo, T>) {}

//// JSON Schema Type

type JSONSchema<T> = T extends number
  ? {
      type: "number" | "integer"
      [keyword: string]: any
    }
  : T extends string
  ? {
      type: "string"
      [keyword: string]: any
    }
  : T extends boolean
  ? {
      type: "boolean"
    }
  : T extends undefined | null
  ? {
      type: "null"
    }
  : T extends any[]
  ? {
      type: "array"
      items: JSONSchema<T[0]>
      [keyword: string]: any
    }
  : {
      type: "object"
      properties: {
        [P in keyof T]: JSONSchema<T[P]>
      }
      required: (keyof T)[]
      [keyword: string]: any
    }