its-valid v1.1.2

its-valid

It's valid! - Typescript validators

Introduction

Validated values

its-valid revolves around two simple primitives

• a validated value Validated<ErrorType, ValueType> is either valid or invalid

  import { Validated } from 'its-valid'
  
  const valid = Validated.ok(99)
  const notValid = Validated.error('Not 99')

• a validation rule is a function from a value of type A to a validated value of type Validated<ErrorType, B> and proves something about your value of type A

  import { Validated, ValidationRule } from 'its-valid'
  
  // Returns the first value of an array (if it exists)
  const firstValue: ValidationRule<number[], string, number> = (ns: number[]) => {
    if (v.length > 0) {
      return Validated.ok(v[0])
    } else {
      return Validated.error('Array is empty')
    }
  }

There can be many reasons why a certain value is not valid. When checking a Person, for instance, we want to verify that each field is valid:

type Person = {
  name: string,
  age: number,
  hasDriversLicense: boolean
}

const validatedPerson = Validated.combine({
  name: Validated.error<string, string>('Not a valid name'),
  age: Validated.ok<Error, number>(new Error()),
  hasDriversLicense: Validated.ok<string, boolean>(true)
})

Type inference works well enough that Typescript can figure out that validatedPerson is a Validated<string | Error, Person>.

Check the structure of an object