@typescript-runtime-schema/is

is function to type guard against given type. To be used in conjunction with @typescript-runtime-schema/transform

Installation

Using npm:

npm install @typescript-runtime-schema/is

Using yarn:

yarn add @typescript-runtime-schema/is

Notes

For this library to work the intended way you also need to add the transform function as a dependency and use it.

npm install @typescript-runtime-schema/transform -D

For how to use & setup the typescript transformer, please see Usage section of @typescript-runtime-schema/transform

Usage

Use the default exported is function to validate that a certain value conforms to a certain type.

The is functions accepts a generic type as a type parameter and will type guard the value provided

Examples

// Basic example
import is from '@typescript-runtime-schema/library'

if(is<string>("Any human can tell this is a string, but a mere compiler won't know because it is cast" as any)) {
  console.log('Safe string zone')
} else {
  console.log('Report issues at https://github.com/simonlovesyou/typescript-runtime-schema/issues')
}

It supports all type primitives (except unknown & never, because it wouldn't really make sense):

• boolean
• number
• string
• array
• tuple
• any
• void
• null
• undefined
• object

The library supports heritage, intersections & unions

import is from '@typescript-runtime-schema/library'

type Animal = { type: 'vertebrates' | 'invertebrates' } & { cute: boolean }

interface Human extends Animal {
  name: string
  age: number
  handedness: 'left' | 'right' | 'ambidextrous'
}

type Alien = { numberOfTentacles: number }

const person = {
  name: 'Simon',
  age: 28,
  handedness: 'right',
  // cute: true /* Cuteness is in the eye of the beholder */ 
}

if(is<Alien | Human>(person as any)) {
  console.log("Alien or Human")
} else {
  console.log("Not a Human or Alien")
}

API

is

Default export.

Signature

function is<T extends Serializable>(value: any) => value is T;

Type Parameters

Name	Constraint	Default value	Description
T	Serializeable	N/A	The type we are type guarding against. Must be a serializeable value

Serializeable

type Serializeable = string | number | boolean | null | Record<string, Serializeable> | Serializeable[];

Parameters

Name	Constraint	Default value	Description
value	N/A	N/A	The value we are type guarding

Returns

boolean: value is T

License

MIT License Copyright (c) 2021 Simon Johansson

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice (including the next paragraph) shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.