Predicates Validator

Allows you to chain together multiple predicate functions which, when evaluated will return a combined validation result.

API

The API for the two validators are the same, the only thing that differs is the return type from the validate function.

Object Validator

This version of the validator will return a discriminatave union object which will allow you to easily differentiate between an error and a success result. The property that will be the basis of the discriminated union is _tag, and it will be equal to either success or error.

Monoid Validator

This validator will return an Either object (as defined by fp-ts, as this is the package that is used in this project). It's return types if an error will be of type string[], which will be the list of error messages, whereas if it's a successful validation then the value will be of type unknown[]. This is because the predicates validator will simply return all of the values that were passed into the chain.

Standard Functions

getObjectValidator() => ObjectValidator

This will return an ObjectValidator that you can then chain predicate validation functions to, before validating it.

Example:

import { getObjectValidator } from 'predicate-validator';
const validationResult = getObjectValidator().validate()

getMonoidValidator() => MonoidValidator

This will return a MonoidValidator that you can then chain predicate validation functions to, before validating it.

Example:

import { getMonoidValidator } from 'predicate-validator';
const validationResult = getMonoidValidator().validate();

Validator Functions

These functions are available on a Validator instance. You can invoke them in the following way:

import { getObjectValidator } from 'predicate-validator';

const validator = getObjectValidator()
  .add("test", val => val.length > 1, "the inputted value must have at least one character")
  .add("test", val => val.length < 30, "the inputted value must not exceed 30 characters")
  .validate();

add(inputVal: unknown, predicateFn: (val: unknown) => boolean, errorMessage: string) => Validator

Parameters:

• inputVal: unknown - this can be any value that you wish to perform validation against.
• predicateFn: (val: unknown) => boolean - this function will be executed using the input value to determine if it should pass validation.
• errorMessage: string - this error message will be present in the errors array if the predicate function fails.

Returns:

• Validator - The object that this function was invoked on will be returned, to allow for chaining.

validate() => ValidationResult

Returns:

• ValidationResult - this will either be a success or error object, depending on the type of validator you have invoked this on. If it is a MonoidValidator then you will be returned with an Either object (as defined here). If it is an ObjectValidator then you will be returned with an object that has a discriminated union property (the property is _tag). You can also use the helper functions listed below to extract the values if you don't want to do anything else with the result.

If you want to work directly with the ObjectValidator/MonoidValidator API's, instead of using a function such as getObjectValidator() or getMonoidValidator() then you can import the individual files directly:

import { createValidator, isSuccess, getResults } from 'predicate-validation/lib/objectValidator'

OR

import { createValidator, isSuccess, getResults } from 'predicate-validation/lib/monoidValidator'

Helper Functions

These helper functions will work in the same way with both the Object Validator and the Monoid Validator.

isError(ValidationResult) => boolean

This is the same API in both objectValidator and monoidValidator so you must directly import the functions from the objectValidator/monoidValidator directly to use.

Examples:

import { createValidator, isError } from 'predicate-validation/lib/objectValidator';

const input = 10;
const validationResultSuccess = createValidator()
  .add(input, val => val > 0, "The inputted value should be a positive number")
  .validate()

console.log(isError(validationResultSuccess)) // => false

import { createValidator, isError } from 'predicate-validation/lib/objectValidator';

const input = 10;
const validationResultSuccess = createValidator()
  .add(input, val => val > 20, "The inputted value should be greater than 20")
  .validate()

console.log(isError(validationResultSuccess)) // => true

isSuccess(ValidationResult) => boolean

This is the same API in both objectValidator and monoidValidator so you must directly import the functions from the objectValidator/monoidValidator directly to use.

Examples:

import { createValidator, isSuccess } from 'predicate-validation/lib/objectValidator';

const input = 10;
const validationResultSuccess = createValidator()
  .add(input, val => val > 0, "The inputted value should be a positive number")
  .validate()

console.log(isSuccess(validationResultSuccess)) // => true

import { createValidator, isSuccess } from 'predicate-validation/lib/objectValidator';

const input = 10;
const validationResultSuccess = createValidator()
  .add(input, val => val > 20, "The inputted value should be greater than 20")
  .validate()

console.log(isSuccess(validationResultSuccess)) // => false

getErrors(ValidationResult) => string[]

This is the same API in both objectValidator and monoidValidator so you must directly import the functions from the objectValidator/monoidValidator directly to use.

If the passed validationResult is a success result then you will be returned an empty array, otherwise you will be returned an array of error messages that were encountered.

Example:

import { createValidator, getErrors } from 'predicate-validation/lib/objectValidator';

const input = 10;
const validationResult = createValidator()
  .add(input, val => val > 0, "The inputted value should be a positive number")
  .add(input, val => val > 20, "The inputted value should be greater than 20") // => ERROR
  .validate();

console.log(getErrors(validationResult)); // => ["The inputted value should be greater than 20"]

getResults(ValidationResult) => unknown[]

This is the same API in both objectValidator and monoidValidator so you must directly import the functions from the objectValidator/monoidValidator directly to use.

As defined by the Either pattern, a result can only be either a success or a failure. For this reason if there are any errors among the validation then this package will not return any results (even if there are successful checks within the chain).

Example:

import { createValidator, getResults } from 'predicate-validation/lib/objectValidator';

const input = 10;
const validationResult = createValidator()
  .add(input, val => val > 0, "The inputted value should be a positive number") // => SUCCESS
  .add(input, val => val > 20, "The inputted value should be greater than 20") // => ERROR
  .validate();

console.log(getResults(validationResult)); // => []

Example:

import { createValidator, getErrors } from 'predicate-validation/lib/objectValidator';

const name = "Angela";
const age = 28;

const validationResult = createValidator()
  .add(name, val => !!val, "A valid name of at least 1 character has to be passed") // => SUCCESS
  .add(age, val => val > 18, "A user has to be at least 18 to use the service") // => SUCCESS
  .validate();

console.log(getResults(validationResult)); // => ["Angela", 28]