ajv.addKeyword({
  keyword: "range",
  type: "number",
  macro: ([minimum, maximum]) => ({minimum, maximum}), // schema with keywords minimum and maximum
  // metaSchema: the same as in the example above
})

ajv.addKeyword({
  keyword: "range",
  type: "number",
  compile([min, max], parentSchema) {
    return parentSchema.exclusiveRange === true
      ? (data) => data > min && data < max
      : (data) => data >= min && data <= max
  },
  errors: false,
  metaSchema: {
    // schema to validate keyword value
    type: "array",
    items: [{type: "number"}, {type: "number"}],
    minItems: 2,
    additionalItems: false,
  },
})

const schema = {
  range: [2, 4],
  exclusiveRange: true,
}
const validate = ajv.compile(schema)
console.log(validate(2.01)) // true
console.log(validate(3.99)) // true
console.log(validate(2)) // false
console.log(validate(4)) // false

//...
const conf = require('../conf');

const ajv = new Ajv({
    schemaId: 'auto',
    allErrors: true,
    verbose: true,
});

ajv.addMetaSchema(require('ajv/lib/refs/json-schema-draft-04.json'));
ajv.addMetaSchema(require('ajv/lib/refs/json-schema-draft-06.json'));

function URIfromId(id) {
    return url.parse(id).path;
}



//...

import {_, nil, KeywordCxt} from Ajv

ajv.addKeyword({
  keyword: "range",
  type: "number",
  code(cxt: KeywordCxt) {
    const {schema, parentSchema, data} = cxt
    const [min, max] = schema
    const eq: Code = parentSchema.exclusiveRange ? _`=` : nil
    cxt.fail(_`${data} <${eq} ${min} || ${data} >${eq} ${max}`)
  },
  metaSchema: {
    type: "array",
    items: [{type: "number"}, {type: "number"}],
    minItems: 2,
    additionalItems: false,
  },
})

const ajv = new Ajv()

ajv.addKeyword({
  keyword: "idExists",
  async: true,
  type: "number",
  validate: checkIdExists,
})

async function checkIdExists(schema, data) {
  // this is just an example, you would want to avoid SQL injection in your code
  const rows = await sql(`SELECT id FROM ${schema.table} WHERE id = ${data}`)
  return !!rows.length // true if record is found
}

const schema = {
  $async: true,
  properties: {
    userId: {
      type: "integer",
      idExists: {table: "users"},
    },
    postId: {
      type: "integer",
      idExists: {table: "posts"},
    },
  },
}

const validate = ajv.compile(schema)

validate({userId: 1, postId: 19})
  .then(function (data) {
    console.log("Data is valid", data) // { userId: 1, postId: 19 }
  })
  .catch(function (err) {
    if (!(err instanceof Ajv.ValidationError)) throw err
    // data is invalid
    console.log("Validation errors:", err.errors)
  })