In TypeScript, how to generally check the instanceof of an object variable? [duplicate]

I want to check if the obj object variable has all the properties of the Person interface.

interface Person { name: string; age: number; } const jsonObj = `{ name: "John Doe", age: 30, }`; const obj: Person = JSON.parse(jsonObj); const isPerson = obj instanceof Person; // Person is not defined console.log(isPerson); // true 

When I execute this code, it yield Person in not defined!

I would expect the code to log true as the obj is an instance of Person.

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Answer Update: Alternative Working Solution Using zod Library

TypeScript works only in compile-time, but instanceof is a runtime thing. You can't use on a type, because types doesn't exist in javascript.

You can use a validator library like zod. Then, you can infer the ("TypeScript") type of the object and validate it with zod.

Per example,

import { z } from 'zod'; export const ItemSchema = z.object({ name: z.string(), description: z.string(), productServiceId: z.number().optional(), }); export type Item = z.infer<typeof ItemSchema>; const validateItems = (items: Item[]) => { const ItemSchemaArray = z.array(ItemSchema); // This line below will throw an error if the validation failed ItemSchemaArray.parse(items); }; 

Konrad referenced this library in the comments below.

Thank you, @Konrad!