Ajv extra is a drop in replacement for ajv with extra goods.

Installation

const Ajv = require('@geoblink/ajv-extra')
const ajv = new Ajv({ allErrors: true })

const schema = { /*** a valid JSON schema ***/ }
validator = ajv.compile(schema)

const isValid = validator({ /*** JSON object to be validated ***/})

OneOfByKey

Sometimes the schema is parametrized by some information. For example:

const schema = {
  type: 'object',
  required: ['data'],
  properties: {
    data: {
      oneOf: [
        {
          type: 'object',
          properties: {
            origin: {
              enum: ['external']
            },
            /** some external properties **/
          }
        },
        {
          type: 'object',
          properties: {
            origin: {
              enum: ['internal']
            },
            /** some external properties **/
          }
        },
      ]
    }
  }
}

In the previous example, we receive data that can be either internal or external with a schema that depends on origin. This schema is nice to work with because data is always present. Depending on the origin we'll have one or the other.

However, there is a big hindrance. Logs are really ugly. If we are given:

const obj = {
  data: {
    origin: 'internal',
    /** wrong properties for internal **/
  }
}

ajv has will show the logs for internal and external, although we are only interested in the internal properties. To solve this problem, we can use oneOfByKey which has a very similar syntax

const schema = {
  type: 'object',
  required: ['data'],
  properties: {
    data: {
      oneOfByKey: {
        key: 'origin',
        oneOf: [
          {
            type: 'object',
            properties: {
              origin: {
                enum: ['external']
              },
              /** some external properties **/
            }
          },
          {
            type: 'object',
            properties: {
              origin: {
                enum: ['internal']
              },
              /** some external properties **/
            }
          },
        ]
      }
    }
  }
}

Now the validator knows that we are only interested in errors for internal properties