An npm library for checking deep types via type predicates.
npm install ts-type-it> A Typescript utility for checking types at runtime. No build steps, clear and simple syntax.
---
``sh`
npm i ts-type-it
!demo
---
`ts
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.
---
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.
type-it also supports any class you define, with zero extra code. For example:
`ts
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.
---
You can type-check against literals (again, arbitrarily nested) and everything will still work:
`ts
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.
---
Unions can be expressed and checked via the Union keyword:
`ts
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.
---
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).