Advanced Object Validation

With the composable nature of Strickland, it is very easy to perform advanced object validation. If our person object might be null in the input, we could use required to validate that it isn't null. And since validators are just functions, we could even write a custom validator to ensure that a person named 'Stanford Strickland' must be born in 1925.

import validate, {
    objectProps, required, length, range, every
} from 'strickland';

// Define the rules for first name, last name, and birthYear
const personPropsValidator = objectProps({
    firstName: every([
        length(2, 20)
    lastName: every([
        length(2, 20)
    birthYear: range(1900, 2018)

function stanfordStricklandBornIn1925(person) {
    if (!person) {
        // If there's no person provided, return valid and
        // rely on `required` to ensure a person exists
        return true;

    const {firstName, lastName} = person;

    if (firstName === 'Stanford' && lastName === 'Strickland') {
        return (person.birthYear === 1925);

    return true;

const personValidator = every([

// Create a person
const person = {
    firstName: 'Stanford',
    lastName: 'Strickland',
    birthYear: 1925

const result = validate(personValidator, person);

In this example, the following will be validated (in this order):

  1. The person is not empty

  2. The person props are validated:

    1. firstName is not empty

    2. firstName has a length between 2 and 20

    3. lastName is not empty

    4. lastName has a length between 2 and 20

    5. birthYear is between 1900 and 2018

  3. stanfordStricklandBornIn1925 is validated

Here are some notes should anything have been invalid:

  1. If the person was empty, neither the object props nor stanfordStricklandBornIn1925 would be validated

  2. If the firstName prop was empty, its length would not be validated

  3. If the lastName prop was empty, its length would not be validated

  4. If the firstName, lastName, or birthYear props were invalid, stanfordStricklandBornIn1925 would not be validated

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