typescript-is-type

A TypeScript-safe runtime type check function

Network requests responses or JSON based data doesn't allow TypeScript to perform compile-time checks. You can cast the response but it doesn't give you the confidence that the data is an instance of the desired type.

This simple one-function package allows you to perform both TypeScript-safe and runtime-safe data check.

If one of the keys to be checked is undefined than the check doesn't pass (it's not based on hasOwnProperty).

# isntall it with
npm install --save-dev typescript-is-type

is<string>("Hello world", "length"); // true
is<string>("Hello world", "concat"); // TS compile error, "concat" isn't a key of string
is<string>(JSON.parse(JSON.stringify("Hello world")), "length"); // true

That's the function signature

function is<Type>(instance: any, keys: keyof Type | (keyof Type)[]): instance is Type;

A more explanatory example

import { is } from "typescript-is-type";

interface Car {
  power: number;
}
interface FuelCar extends Car {
  tank: number;
}
interface ElectricCar extends Car {
  battery: number;
  singlePedalDrive: boolean;
}

is<ElectricCar>(
  JSON.parse(
    JSON.stringify({
      power: 450,
      tank: 60
    })
  ),
  "battery"
); // false

Remember that it's up to you to decide the keys to be checked to avoid every false positive/negative.

is<ElectricCar>({
  power: 450,
  tank: 60
}), "power") // true 🤔
is<ElectricCar>({
  power: 450,
  tank: 60
}), ["power", "battery"]) // false 🎉

Contributors

Thanks goes to these wonderful people (emoji key):

Stefano Magni 💻 ⚠️

This project follows the all-contributors specification. Contributions of any kind welcome!