Custom JSON-Schema keywords for Ajv validator

Please note: This readme file is for ajv-keywords v5.0.0 that should be used with ajv v8.

ajv-keywords v3 should be used with ajv v6.

• Install
• Usage
• Keywords
  • Types
    • typeof
    • instanceof⁺
  • Keywords for numbers
    • range and exclusiveRange
  • Keywords for strings
    • regexp
    • transform^*
  • Keywords for arrays
    • uniqueItemProperties⁺
  • Keywords for objects
    • allRequired
    • anyRequired
    • oneRequired
    • patternRequired
    • prohibited
    • deepProperties
    • deepRequired
    • dynamicDefaults^*+
  • Keywords for all types
    • select/selectCases/selectDefault
• Security contact
• Open-source software support
• License

^* - keywords that modify data ⁺ - keywords that are not supported in standalone validation code

To install version 4 to use with Ajv v7:

npm install ajv-keywords

To add all available keywords:

const Ajv = require("ajv")
const ajv = new Ajv()
require("ajv-keywords")(ajv)

ajv.validate({instanceof: "RegExp"}, /.*/) // true
ajv.validate({instanceof: "RegExp"}, ".*") // false

To add a single keyword:

require("ajv-keywords")(ajv, "instanceof")

To add multiple keywords:

require("ajv-keywords")(ajv, ["typeof", "instanceof"])

To add a single keyword directly (to avoid adding unused code):

require("ajv-keywords/dist/keywords/select")(ajv, opts)

To add all keywords via Ajv options:

const ajv = new Ajv({keywords: require("ajv-keywords/dist/definitions")(opts)})

To add one or several keywords via options:

const ajv = new Ajv({
  keywords: [
    require("ajv-keywords/dist/definitions/typeof")(),
    require("ajv-keywords/dist/definitions/instanceof")(),
    // select exports an array of 3 definitions - see "select" in docs
    ...require("ajv-keywords/dist/definitions/select")(opts),
  ],
})

opts is an optional object with a property defaultMeta - URI of meta-schema to use for keywords that use subschemas (select and deepProperties). The default is "http://json-schema.org/schema".

Based on JavaScript typeof operation.

The value of the keyword should be a string ("undefined", "string", "number", "object", "function", "boolean" or "symbol") or an array of strings.

To pass validation the result of typeof operation on the value should be equal to the string (or one of the strings in the array).

ajv.validate({typeof: "undefined"}, undefined) // true
ajv.validate({typeof: "undefined"}, null) // false
ajv.validate({typeof: ["undefined", "object"]}, null) // true

Based on JavaScript instanceof operation.

The value of the keyword should be a string ("Object", "Array", "Function", "Number", "String", "Date", "RegExp" or "Promise") or an array of strings.

To pass validation the result of data instanceof ... operation on the value should be true:

ajv.validate({instanceof: "Array"}, []) // true
ajv.validate({instanceof: "Array"}, {}) // false
ajv.validate({instanceof: ["Array", "Function"]}, function () {}) // true

You can add your own constructor function to be recognised by this keyword:

class MyClass {}
const instanceofDef = require("ajv-keywords/dist/definitions/instanceof")
instanceofDef.CONSTRUCTORS.MyClass = MyClass
ajv.validate({instanceof: "MyClass"}, new MyClass()) // true

Please note: currently instanceof is not supported in standalone validation code - it has to be implemented as code keyword to support it (PR is welcome).

Syntax sugar for the combination of minimum and maximum keywords (or exclusiveMinimum and exclusiveMaximum), also fails schema compilation if there are no numbers in the range.

The value of these keywords must be an array consisting of two numbers, the second must be greater or equal than the first one.

If the validated value is not a number the validation passes, otherwise to pass validation the value should be greater (or equal) than the first number and smaller (or equal) than the second number in the array.

const schema = {type: "number", range: [1, 3]}
ajv.validate(schema, 1) // true
ajv.validate(schema, 2) // true
ajv.validate(schema, 3) // true
ajv.validate(schema, 0.99) // false
ajv.validate(schema, 3.01) // false

const schema = {type: "number", exclusiveRange: [1, 3]}
ajv.validate(schema, 1.01) // true
ajv.validate(schema, 2) // true
ajv.validate(schema, 2.99) // true
ajv.validate(schema, 1) // false
ajv.validate(schema, 3) // false

This keyword allows to use regular expressions with flags in schemas, and also without "u" flag when needed (the standard pattern keyword does not support flags and implies the presence of "u" flag).

This keyword applies only to strings. If the data is not a string, the validation succeeds.

The value of this keyword can be either a string (the result of regexp.toString()) or an object with the properties pattern and flags (the same strings that should be passed to RegExp constructor).

const schema = {
  type: "object",
  properties: {
    foo: {type: "string", regexp: "/foo/i"},
    bar: {type: "string", regexp: {pattern: "bar", flags: "i"}},
  },
}

const validData = {
  foo: "Food",
  bar: "Barmen",
}

const invalidData = {
  foo: "fog",
  bar: "bad",
}

This keyword allows a string to be modified during validation.

This keyword applies only to strings. If the data is not a string, the transform keyword is ignored.

A standalone string cannot be modified, i.e. data = 'a'; ajv.validate(schema, data);, because strings are passed by value

Supported transformations:

• trim: remove whitespace from start and end
• trimStart/trimLeft: remove whitespace from start
• trimEnd/trimRight: remove whitespace from end
• toLowerCase: convert to lower case
• toUpperCase: convert to upper case
• toEnumCase: change string case to be equal to one of enum values in the schema

Transformations are applied in the order they are listed.

Note: toEnumCase requires that all allowed values are unique when case insensitive.

Example: multiple transformations

require("ajv-keywords")(ajv, "transform")

const schema = {
  type: "array",
  items: {
    type: "string",
    transform: ["trim", "toLowerCase"],
  },
}

const data = ["  MixCase  "]
ajv.validate(schema, data)
console.log(data) // ['mixcase']

Example: enumcase

require("ajv-keywords")(ajv, ["transform"])

const schema = {
  type: "array",
  items: {
    type: "string",
    transform: ["trim", "toEnumCase"],
    enum: ["pH"],
  },
}

const data = ["ph", " Ph", "PH", "pH "]
ajv.validate(schema, data)
console.log(data) // ['pH','pH','pH','pH']

The keyword allows to check that some properties in array items are unique.

This keyword applies only to arrays. If the data is not an array, the validation succeeds.

The value of this keyword must be an array of strings - property names that should have unique values across all items.

const schema = {
  type: "array",
  uniqueItemProperties: ["id", "name"],
}

const validData = [{id: 1}, {id: 2}, {id: 3}]

const invalidData1 = [
  {id: 1},
  {id: 1}, // duplicate "id"
  {id: 3},
]

const invalidData2 = [
  {id: 1, name: "taco"},
  {id: 2, name: "taco"}, // duplicate "name"
  {id: 3, name: "salsa"},
]

This keyword is contributed by @blainesch.

Please note: currently uniqueItemProperties is not supported in standalone validation code - it has to be implemented as code keyword to support it (PR is welcome).

This keyword allows to require the presence of all properties used in properties keyword in the same schema object.

This keyword applies only to objects. If the data is not an object, the validation succeeds.

The value of this keyword must be boolean.

If the value of the keyword is false, the validation succeeds.

If the value of the keyword is true, the validation succeeds if the data contains all properties defined in properties keyword (in the same schema object).

If the properties keyword is not present in the same schema object, schema compilation will throw exception.

const schema = {
  type: "object",
  properties: {
    foo: {type: "number"},
    bar: {type: "number"},
  },
  allRequired: true,
}

const validData = {foo: 1, bar: 2}
const alsoValidData = {foo: 1, bar: 2, baz: 3}

const invalidDataList = [{}, {foo: 1}, {bar: 2}]

This keyword allows to require the presence of any (at least one) property from the list.

This keyword applies only to objects. If the data is not an object, the validation succeeds.

The value of this keyword must be an array of strings, each string being a property name. For data object to be valid at least one of the properties in this array should be present in the object.

const schema = {
  type: "object",
  anyRequired: ["foo", "bar"],
}

const validData = {foo: 1}
const alsoValidData = {foo: 1, bar: 2}

const invalidDataList = [{}, {baz: 3}]

This keyword allows to require the presence of only one property from the list.

This keyword applies only to objects. If the data is not an object, the validation succeeds.

The value of this keyword must be an array of strings, each string being a property name. For data object to be valid exactly one of the properties in this array should be present in the object.

const schema = {
  type: "object",
  oneRequired: ["foo", "bar"],
}

const validData = {foo: 1}
const alsoValidData = {bar: 2, baz: 3}

const invalidDataList = [{}, {baz: 3}, {foo: 1, bar: 2}]

This keyword allows to require the presence of properties that match some pattern(s).

This keyword applies only to objects. If the data is not an object, the validation succeeds.

The value of this keyword should be an array of strings, each string being a regular expression. For data object to be valid each regular expression in this array should match at least one property name in the data object.

If the array contains multiple regular expressions, more than one expression can match the same property name.

const schema = {
  type: "object",
  patternRequired: ["f.*o", "b.*r"],
}

const validData = {foo: 1, bar: 2}
const alsoValidData = {foobar: 3}

const invalidDataList = [{}, {foo: 1}, {bar: 2}]

This keyword allows to prohibit that any of the properties in the list is present in the object.

This keyword applies only to objects. If the data is not an object, the validation succeeds.

The value of this keyword should be an array of strings, each string being a property name. For data object to be valid none of the properties in this array should be present in the object.

const schema = {
  type: "object",
  prohibited: ["foo", "bar"],
}

const validData = {baz: 1}
const alsoValidData = {}

const invalidDataList = [{foo: 1}, {bar: 2}, {foo: 1, bar: 2}]

Please note: {prohibited: ['foo', 'bar']} is equivalent to {not: {anyRequired: ['foo', 'bar']}} (i.e. it has the same validation result for any data).

This keyword allows to validate deep properties (identified by JSON pointers).

This keyword applies only to objects. If the data is not an object, the validation succeeds.

The value should be an object, where keys are JSON pointers to the data, starting from the current position in data, and the values are JSON schemas. For data object to be valid the value of each JSON pointer should be valid according to the corresponding schema.

const schema = {
  type: "object",
  deepProperties: {
    "/users/1/role": {enum: ["admin"]},
  },
}

const validData = {
  users: [
    {},
    {
      id: 123,
      role: "admin",
    },
  ],
}

const alsoValidData = {
  users: {
    1: {
      id: 123,
      role: "admin",
    },
  },
}

const invalidData = {
  users: [
    {},
    {
      id: 123,
      role: "user",
    },
  ],
}

const alsoInvalidData = {
  users: {
    1: {
      id: 123,
      role: "user",
    },
  },
}

This keyword allows to check that some deep properties (identified by JSON pointers) are available.

This keyword applies only to objects. If the data is not an object, the validation succeeds.

The value should be an array of JSON pointers to the data, starting from the current position in data. For data object to be valid each JSON pointer should be some existing part of the data.

const schema = {
  type: "object",
  deepRequired: ["/users/1/role"],
}

const validData = {
  users: [
    {},
    {
      id: 123,
      role: "admin",
    },
  ],
}

const invalidData = {
  users: [
    {},
    {
      id: 123,
    },
  ],
}

See json-schema-org/json-schema-spec#203 for an example of the equivalent schema without deepRequired keyword.

Please note: these keywords are deprecated. It is recommended to use OpenAPI discriminator keyword supported by Ajv v8 instead of select.

These keywords allow to choose the schema to validate the data based on the value of some property in the validated data.

These keywords must be present in the same schema object (selectDefault is optional).

The value of select keyword should be a $data reference that points to any primitive JSON type (string, number, boolean or null) in the data that is validated. You can also use a constant of primitive type as the value of this keyword (e.g., for debugging purposes).

The value of selectCases keyword must be an object where each property name is a possible string representation of the value of select keyword and each property value is a corresponding schema (from draft-06 it can be boolean) that must be used to validate the data.

The value of selectDefault keyword is a schema (also can be boolean) that must be used to validate the data in case selectCases has no key equal to the stringified value of select keyword.

The validation succeeds in one of the following cases:

• the validation of data using selected schema succeeds,
• none of the schemas is selected for validation,
• the value of select is undefined (no property in the data that the data reference points to).

If select value (in data) is not a primitive type the validation fails.

This keyword correctly tracks evaluated properties and items to work with unevaluatedProperties and unevaluatedItems keywords - only properties and items from the subschema that was used (one of selectCases subschemas or selectDefault subschema) are marked as evaluated.

Please note: these keywords require Ajv $data option to support $data reference.

require("ajv-keywords")(ajv, "select")

const schema = {
  type: "object",
  required: ["kind"],
  properties: {
    kind: {type: "string"},
  },
  select: {$data: "0/kind"},
  selectCases: {
    foo: {
      required: ["foo"],
      properties: {
        kind: {},
        foo: {type: "string"},
      },
      additionalProperties: false,
    },
    bar: {
      required: ["bar"],
      properties: {
        kind: {},
        bar: {type: "number"},
      },
      additionalProperties: false,
    },
  },
  selectDefault: {
    propertyNames: {
      not: {enum: ["foo", "bar"]},
    },
  },
}

const validDataList = [
  {kind: "foo", foo: "any"},
  {kind: "bar", bar: 1},
  {kind: "anything_else", not_bar_or_foo: "any value"},
]

const invalidDataList = [
  {kind: "foo"}, // no property foo
  {kind: "bar"}, // no property bar
  {kind: "foo", foo: "any", another: "any value"}, // additional property
  {kind: "bar", bar: 1, another: "any value"}, // additional property
  {kind: "anything_else", foo: "any"}, // property foo not allowed
  {kind: "anything_else", bar: 1}, // property bar not allowed
]

This keyword allows to assign dynamic defaults to properties, such as timestamps, unique IDs etc.

This keyword only works if useDefaults options is used and not inside anyOf keywords etc., in the same way as default keyword treated by Ajv.

The keyword should be added on the object level. Its value should be an object with each property corresponding to a property name, in the same way as in standard properties keyword. The value of each property can be:

• an identifier of dynamic default function (a string)
• an object with properties func (an identifier) and args (an object with parameters that will be passed to this function during schema compilation - see examples).

The properties used in dynamicDefaults should not be added to required keyword in the same schema (or validation will fail), because unlike default this keyword is processed after validation.

There are several predefined dynamic default functions:

• "timestamp" - current timestamp in milliseconds
• "datetime" - current date and time as string (ISO, valid according to date-time format)
• "date" - current date as string (ISO, valid according to date format)
• "time" - current time as string (ISO, valid according to time format)
• "random" - pseudo-random number in [0, 1) interval
• "randomint" - pseudo-random integer number. If string is used as a property value, the function will randomly return 0 or 1. If object { func: 'randomint', args: { max: N } } is used then the default will be an integer number in [0, N) interval.
• "seq" - sequential integer number starting from 0. If string is used as a property value, the default sequence will be used. If object { func: 'seq', args: { name: 'foo'} } is used then the sequence with name "foo" will be used. Sequences are global, even if different ajv instances are used.

const schema = {
  type: "object",
  dynamicDefaults: {
    ts: "datetime",
    r: {func: "randomint", args: {max: 100}},
    id: {func: "seq", args: {name: "id"}},
  },
  properties: {
    ts: {
      type: "string",
      format: "date-time",
    },
    r: {
      type: "integer",
      minimum: 0,
      exclusiveMaximum: 100,
    },
    id: {
      type: "integer",
      minimum: 0,
    },
  },
}

const data = {}
ajv.validate(data) // true
data // { ts: '2016-12-01T22:07:28.829Z', r: 25, id: 0 }

const data1 = {}
ajv.validate(data1) // true
data1 // { ts: '2016-12-01T22:07:29.832Z', r: 68, id: 1 }

ajv.validate(data1) // true
data1 // didn't change, as all properties were defined

When using the useDefaults option value "empty", properties and items equal to null or "" (empty string) will be considered missing and assigned defaults. Use allOf compound keyword to execute dynamicDefaults before validation.

const schema = {
  type: "object",
  allOf: [
    {
      dynamicDefaults: {
        ts: "datetime",
        r: {func: "randomint", args: {min: 5, max: 100}},
        id: {func: "seq", args: {name: "id"}},
      },
    },
    {
      properties: {
        ts: {
          type: "string",
        },
        r: {
          type: "number",
          minimum: 5,
          exclusiveMaximum: 100,
        },
        id: {
          type: "integer",
          minimum: 0,
        },
      },
    },
  ],
}

const data = {ts: "", r: null}
ajv.validate(data) // true
data // { ts: '2016-12-01T22:07:28.829Z', r: 25, id: 0 }

You can add your own dynamic default function to be recognised by this keyword:

const uuid = require("uuid")

const def = require("ajv-keywords/dist/definitions/dynamicDefaults")
def.DEFAULTS.uuid = () => uuid.v4

const schema = {
  dynamicDefaults: {id: "uuid"},
  properties: {id: {type: "string", format: "uuid"}},
}

const data = {}
ajv.validate(schema, data) // true
data // { id: 'a1183fbe-697b-4030-9bcc-cfeb282a9150' };

const data1 = {}
ajv.validate(schema, data1) // true
data1 // { id: '5b008de7-1669-467a-a5c6-70fa244d7209' }

You also can define dynamic default that accept parameters, e.g. version of uuid:

const uuid = require("uuid")

function getUuid(args) {
  const version = "v" + ((arvs && args.v) || "4")
  return uuid[version]
}

const def = require("ajv-keywords/dist/definitions/dynamicDefaults")
def.DEFAULTS.uuid = getUuid

const schema = {
  dynamicDefaults: {
    id1: "uuid", // v4
    id2: {func: "uuid", v: 4}, // v4
    id3: {func: "uuid", v: 1}, // v1
  },
}

Please note: dynamic default functions are differentiated by the number of parameters they have (function.length). Functions that do not expect default must have one non-optional argument so that function.length > 0.

dynamicDefaults is not supported in standalone validation code.

To report a security vulnerability, please use the Tidelift security contact. Tidelift will coordinate the fix and disclosure.

Please do NOT report security vulnerabilities via GitHub issues.

Ajv-keywords is a part of Tidelift subscription - it provides a centralised support to open-source software users, in addition to the support provided by software maintainers.

MIT