Letype

Type checker that uses native data types.

Letype is simple and small (1kB minified + gzipped) type checker library that can validate any JS data types and structures as well as any custom ones.

Features

• Uses native JS data types.
• Can validate type structures.
• Supports regex validation as a type.
• Supports custom types.
• Small in size.

Installation

To install the stable version:

npm install --save letype

This assumes you are using npm as your package manager.

If you're not, you can access these files on unpkg (letype.min.js is the file you're probalby after), download them, or point your package manager to them.

Browser Compatibility

Letype.js currently is compatible with all modern browsers.

Example usage

import { types, check } from 'letype';

check(1, Number); // -> true

check('1', Number); // -> false
// "Type error: `1` is not of type `number`"

check({ counter: 1 }, { counter: Number }); // -> true

check({
  id: 1,
  name: 92942,
  age: '21',
  work: null,
  anythingGoes: 'flamingo',
  date: new Date(),
  regexp: 123,
}, {
  id: Number,
  name: String,
  age: Number,
  role: String,
  anythingGoes: types.Any,
  date: Date,
  regexp: /123/,
}); // -> false
// "Type error: `92942` is not of type `string` in `name`"
// "Type error: `21` is not of type `number` in `age`"
// "Type error: `role` is undefined! Required value of type `string`"
// "Type error: `work` is defined as `null`! But it should not be defined at all!"

All available exports from package:

import {
  types,
  check,
  assert,
} from 'letype';

const {
  Any,
  Or,
  Undefined,
  Custom,
} = types;

List of available functions

• check()
• assert()

Usage of functions

check()

It takes first argument as value that should be checked. Second argument is type that the value should be checked against. It returns boolean (true if valid, false if invalid).

check('John Doe', String); // -> true
check(123, String); // -> false

assert()

It does exactly the same thing as check() function, but with a little difference. If validation fails it throws error.

assert('John Doe', String); // -> true
assert(123, String); // -> Throw

List of available types

Types are meant to be used as data types that does custom validation against given value inside assert() or check() functions.

Types from letype library:

• types.Any
• types.Or(...types)
• types.Undefined
• types.Custom

Types from JavaScript language:

• String
• Number
• Boolean
• Array
• Function
• Date
• RegExp

Types can also be created in structures:

• Typed Arrays
• Typed Objects
• Regular Expressions

Usage of types

types.Any

check('string', Any); // -> true
check(123, Any);      // -> true

types.Or()

check('string', Or(String, Number)); // -> true
check(123, Or(String, Number));  // -> true
check(true, Or(String, Number)); // -> false

types.Undefined

check('string', Undefined);  // -> false
check(undefined, Undefined); // -> true

types.Custom

Custom type is empty and does no checks against anything. It is meant for creating your own custom types.

To do that just extend Custom class and define public parse method that has one parameter - "value". It is value to be checked/validated. parse method should return boolean (true if valid, false if invalid).

For example lets create type that checks if value has first capital letter.

class Capital extends types.Custom {
  parse(value) {
    return value[0] === value[0].toUpperCase();
  }
}

To use it simply pass it in any of assert() or check() functions.

check('John', Capital); // -> true
check('doe', Capital);  // -> false

String

check('123', String); // -> true
check(123, String);   // -> false

Number

check('123', Number); // -> false
check(123, Number);   // -> true

Boolean

check('false', Boolean); // -> false
check(false, Boolean);   // -> true

Array

check('array', Array); // -> false
check([], Array);      // -> true
check([1,2,3], Array); // -> true

Function

check('fn', Function);     // -> false
check(() => {}, Function); // -> true

Date

check('10-12-2020', Date); // -> false
check(new Date('10-12-2020'), Date); // -> true

RegExp

check('A-Z', RegExp); // -> false
check(/A-Z/, RegExp); // -> true

Typed Arrays

check([], [String]);    // -> false
check([1], [String]);   // -> false
check(['1'], [String]); // -> true

Typed Objects

check({}, { name: String }); // -> false
check({ name: 1 }, { name: String }); // -> false
check({ name: 'John' }, { name: String }); // -> true

Regular Expressions

check('a', /A-Z/); // -> false
check('A', /A-Z/); // -> true

---

Motivation

We can get awesome type checking in JS with TS, but that only checks types in compile time.

So I wanted some kind of runtime type checking with types that are already available in JS - not using strings as a types. This feels more JS and more natural.

License

MIT licenced. Copyright © 2020-present, Marcis (Marcisbee) Bergmanis