Transform.ts

Powerful object serialization/deserialization library.

• Easy to use
• Flexible
• Written in TypeScript

How to use

$ npm install transform-ts or $ yarn add transform-ts

Usage

Transformer

Transformer<A,B> has A to B transformation. It also has B to A (inverse) transformation.

Transformation

import $, { Transformer, ValidationResult } from 'transform-ts'

declare const fab: Transformer<A, B>

declare const validA: A
declare const invalidA: A

const result1: ValidationResult<B> = fab.transform(validA) // $.isOk(result1) === true
const result2: ValidationResult<B> = fab.transform(invalidA) // $.isError(result2) === true

const b1: B = fab.transformOrThrow(validA)
const b2: B = fab.transformOrThrow(invalidA) // Throw Error!

Composition

Transformer<A,B> is composable to Tranformer<B,C>.

declare const fab: Transformer<A, B>
declare const fbc: Transformer<B, C>

const fac: Transformer<A, C> = fab.compose(fbc)

Builtin Transformers

• any: Transformer<unknown, unknown>(validate that input value is not undefined or null)
• number: Transformer<unknown, number>
• string: Transformer<unknown, string>
• boolean: Tranformer<unknown, boolean>

const num = $.number.transformOrThrow(123 as unknown)

Transformer Combinators

nullable

converts Transformer<A, B> to Transformer<A | null, B | null>

declare const fab: Transformer<A, B>

const f: Transformer<A | null, B | null> = $.nullable(fab)

optional

converts Transformer<A, B> to Transformer<A | undefined, B | undefined>

declare const fab: Transformer<A, B>

const f: Transformer<A | undefined, B | undefined> = $.optional(fab)

array

converts Transformer<unknown, A> to Transformer<unknown, A[]>

const f: Transformer<unknown, number[]> = $.array($.number)

tuple

const f: Transformer<unknown, [number, string]> = $.tuple($.number, $.string)

obj

const f: Transformer<unknown, { a: number; b: string }> = $.obj({
  a: $.number,
  b: $.string,
})

You can construct complex Transformer with simple transformers and combinators. Try it out!

Example

user.json

{
  "id": 9,
  "name": "a",
  "screenName": "ika",
  "application": {
    "id": 13,
    "name": "V",
    "isAutomated": false
  }
}

import $, { Transformer } from 'transform-ts'

const userTransformer: Transformer<
  unknown,
  {
    id: number
    name: string
    screenName: string
    application: {
      id: number
      name: string
      isAutomated: boolean | undefined
    }
  }
> = $.obj({
  id: $.number,
  name: $.string,
  screenName: $.string,
  application: $.obj({
    id: $.number,
    name: $.string,
    isAutomated: $.optional($.boolean),
  }),
})

const user = userTransformer.transformOrThrow(require('./user.json'))

const userJson = JSON.stringify(userTransformer.invert().transformOrThrow(user))

Custom Transformer

You can write your own transformer.

/*
Transformer requires `A` to `B` and `B` to `A` transformation.
`A` to `B` transformation is a function `(a: A) => ValidationResult<B>`.
You can use `$.ok` and `$.error` to create `ValidationResult`.
Returning `$.ok(value)` represents that transformation is success with `value`.
Returning `$.error(error)` represents that error(s) has occured.
*/
import $, { Transformer, ok } from 'transform-ts'

const stringToDate = Transformer.from<string, Date>(str => ok(new Date(str)))

const date = stringToDate.transformOrThrow('2019-05-01T15:13:34.459Z')
const dateString = stringToDate.inverseTransformOrThrow(new Date())

Using custom transformers, you can transform unknown to any type you like.