Parz

A simple utility for parsing and validating values. The motivation behind is stateless validaton of html input fields.

You can chain multiple validators and parsers with then. If a validator fails, it will keep on validating and return the results for all validators. If a parser fails, it will stop and return all the errors up to that point.

Usage

Start by creating a validator. createValidator expects two functions, one for validation T -> boolean, and one for error handling T -> NonEmptyArray<string>.

import { createValidator } from '@mokd/parz'

const stringOfLength5 = createValidator(
    (str : string) => str.length === 5,
    (str) => [`String is not length 5, it is actually of length ${str.length}`]
)

Once you have a validator, you can do this:

import { startWith, isJust } from '@mokd/parz'

const validationResult = startWith("Hello")
    .then(stringOfLength5)
    .value()

if (isJust(validationResult)) {
    console.log(validationResult.target) // target is string
}

Sometimes, we also want to parse/transform. createParser takes two functions, one TOriginal -> TParsed, and one TOriginal -> NonEmptyArray<string>. To indicate parsing failure, you must return null on failure. If not, you'll have undefined behaviour.

import { createParser } from '@mokd/parz'

const stringToInteger = createParser(
    (str : string) => {
        const res = parseInt(str)
        if (isNaN(res)) return null;
        return res;
    }, 
    (str) => [`${str} cannot be parsed to an integer`]
)

Parsers and validators can be composed:

const onesAndThenZeros = createValidator(
    (str : string) => RegExp(/^10+$/).test(str), 
    (str) => [`${str} must start with a one and end with one or more zeroes`]
)

const stringToInteger = createParser(
    (str : string) => {
        const res = parseInt(str)
        if (isNaN(res)) return null;
        return res;
    }, 
    (str) => [`${str} cannot be parsed to an integer`]
)

const atLeastOneThousand = createValidator(
    (n : number) => n > 1000, 
    (n) => [`${n} must be at least 1000`]
)

const fn = (oneAndZeroes : string) => startWith(oneAndZeroes)
        .then(onesAndThenZeros)
        .then(stringToInteger)
        .then(atLeastOneThousand)
        .value() 
        
const successResult = fn("10000") 

if (isJust(successResult)) {
    console.log(successResult.target) // target is number
    console.log(successResult.original) // original is string
}

const failResult = fn("100")

if (isJust(failResult)) {
    console.log(failResult.errors) // errors is string[], as specified in the second type parameter of startWith
    console.log(failResult.original) // original is string
}

Example for composite values. deflate accepts a Record<string, ParzRes<unknown, unknown>>, and returns an object with mapDeflated, which lets you operate on the ParzOK target values, if and only if all values in the record evaluate to ParzOk. The mapDeflated function returns a ParzRes, which lets you compose additional validators and parsers.

const length = startWith("10").then(stringToInteger).value()
const width = startWith("10").then(stringToInteger).value()
const height = startWith("10").then(stringToInteger).value()

const maybeVolume = deflate({length, width, height}).mapDeflated(x => x.length*x.width*x.height).value()

if (isJust(maybeVolume)) {
    console.log(maybeVolume.target) // value is number
}