const schema = {
  type: "object",
  required: ["foo", "bar"],
  allOf: [
    {
      properties: {
        foo: {type: "integer", minimum: 2},
        bar: {type: "string", minLength: 2},
      },
      additionalProperties: false,
    },
  ],
  errorMessage: {
    type: "data should be an object",
    properties: {
      foo: "data.foo should be integer >= 2",
      bar: "data.bar should be string with length >= 2",
    },
    _: 'data should have properties "foo" and "bar" only',
  },
}

const validate = ajv.compile(schema)
console.log(validate({})) // false
console.log(validate.errors) // processed errors