joi.js

import Joi from 'joi';

const schema = Joi.object({
    a: Joi.string().required(),
    b: Joi.string().required(),
});

const {error: error1} = Joi.validate(null, schema); // "value" must be an object
const {error: error2} = Joi.validate(undefined, schema); // null
const {error: error3} = Joi.validate({}, schema); // child "a" fails because ["a" is required]
const {error: error4} = Joi.validate({a: 'qwerty'}, schema); // child "b" fails because ["b" is required]
const {error: error5} = Joi.validate({a: 'qwerty', b: 'asdfgh'}, schema); // null

console.log('--- 1', error1);
console.log('--- 2', error2);
console.log('--- 3', error3);
console.log('--- 4', error4);
console.log('--- 5', error5);