ts-type-it

> A Typescript utility for checking types at runtime. No build steps, clear and simple syntax.

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Installation

npm i ts-type-it

Screenshot

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Usage

import { typeIt } from "ts-type-it"
 
const value = { x: "foobar" } as any;
 
if (typeIt(value, { x: String })) { // Passes!
 
  x; // TS::{x:string}
}

type-it takes in any value to check, along with a simple type object. It returns a boolean value with full type inference.

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Feature Support

type-it is as powerful as it is simple. It has support for tuples, strings, numbers, literals, booleans, symbols, Promises, Generators, AsyncGenerators, and nested structures, right out-of-the-box.

Classes

type-it also supports any class you define, with zero extra code. For example:

import { typeIt } from "ts-type-it"
 
class MyClass { }
 
const value = {
  x: [{y: new MyClass()}],
  z: Number
} as any;
 
const type = {x:[{y:MyClass}],z:42} as const;
 
if (typeIt(value, type)) {
 
  value; // TS::{x:[{y:MyClass}],z:Number}
}

Note, to use tuples or literals, the keyword 'as const' is needed to prevent Typescript from automatically widening the types. This is how you unlock length-specific tuple validation as well as literal string typing.

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Literals

You can type-check against literals (again, arbitrarily nested) and everything will still work:

import { typeIt } from "ts-type-it"
 
const value = 400 as any;
const type = 42;
 
if (typeIt(value, type)) { // will return false as 400 !== 42
 
  value; // TS::{x:42}
}

This library can be used for validating parameters all the way to validating complex payloads, all with a minimum conceptual overhead. If you know Typescript, you know how to use type-it.

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Unions

Unions can be expressed and checked via the Union keyword:

import { typeIt, Union } from "ts-type-it"
 
const value = 400 as any;
const type = 42;
 
if (typeIt(value, Union(String, {x: Number}))) {
  value; // TS::string|{x:number}
}

Additionally, Union works recursively both on the type and value levels. So having internal types of Union that also utilize Union is just fine.

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Contribution

Contribution is encouraged! If I missed anything, or there's a use-case I didn't consider, definitely feel free to file an issue and/or PR. This project is licensed under the MIT license as most npm packages are. (see license.md).