How to validate a number is even?

[jeffski]

Support plan

• is this issue currently blocking your project? (yes/no): No
• is this issue affecting a production system? (yes/no): No

Context

• node version: 12
• module version: 6
• environment (e.g. node, browser, native): Node
• used with (e.g. hapi application, another framework, standalone, ...): Standalone
• any other relevant information:

How can we help?

I have a use case that requires numeric values to be even. Values are entered via an API request, so I can not use the UI to enforce the numbers. Is there any feature within Joi that would allow me to validate a number is even?

[Adibla]

You can obtain this using custom validation https://github.com/sideway/joi/blob/master/API.md#anycustommethod-description

A simple implementation could be

const Joi = require('joi');

const evenValidation = (value, helpers) => {
    if(value % 2){
        throw new Error('is odd');
    }
    return value;
};

const schema = Joi.number().custom(evenValidation, 'even validation')

schema.validate(30) // valid

schema.validate(29)
/*
{
  value: 29,
  error: [Error [ValidationError]: "value" failed custom validation because is odd] {
    _original: 29,
    details: [ [Object] ]
  }
}
*/