ajv-keywords
Advanced tools
The ajv-keywords package extends AJV (Another JSON Schema Validator) with additional keywords for JSON schema validation. It allows for more complex validation scenarios beyond what is available in the standard JSON Schema.
dynamicDefaults
Allows setting dynamic defaults for properties, such as generating timestamps for createdAt fields.
{"properties": {"createdAt": {"type": "string", "format": "date-time", "default": "dynamic", "dynamicDefault": "datetime"}}}transform
Enables transformation of data before validation. For example, trimming whitespace and converting text to lowercase.
{"properties": {"email": {"type": "string", "transform": ["trim", "toLowerCase"]}}}range
Introduces exclusive range validation for numeric values, allowing for minimum and maximum values to be exclusive.
{"properties": {"age": {"type": "number", "exclusiveRange": true, "minimum": 18, "maximum": 60}}}A JSON Schema validator that supports draft-04/06/07. It's similar to ajv-keywords in providing JSON schema validation but does not offer the same level of keyword extension for custom validation scenarios.
Tiny Validator (tv4) is a lightweight JSON Schema validator that supports draft-04. While it provides basic validation capabilities, it lacks the extensibility and additional keywords provided by ajv-keywords.
Custom JSON-Schema keywords for Ajv validator
Please note: ajv-keywords v4.0.0-beta should be used with ajv v7 (beta)
* - keywords that modify data
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 object with a property defaultMeta - URI of meta-schema to use for keywords that use subschemas (select and deepProperties).
typeofBased 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
instanceofBased 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
range and exclusiveRangeSyntax 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
regexpThis 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",
}
transformThis 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 endtrimStart/trimLeft: remove whitespace from starttrimEnd/trimRight: remove whitespace from endtoLowerCase: convert to lower casetoUpperCase: convert to upper casetoEnumCase: change string case to be equal to one of enum values in the schemaTransformations 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']
uniqueItemPropertiesThe 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.
allRequiredThis 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 } ];
anyRequiredThis 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}]
oneRequiredThis 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}]
patternRequiredThis 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}]
prohibitedThis 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).
deepPropertiesThis 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",
},
},
}
deepRequiredThis 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.
select/selectCases/selectDefaultThese 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:
If select value (in data) is not a primitive type the validation fails.
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 propery foo
{ kind: 'bar' }, // no propery 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
];
dynamicDefaultsThis 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:
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 differented 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.
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.
FAQs
Additional JSON-Schema keywords for Ajv JSON validator
The npm package ajv-keywords receives a total of 40,003,782 weekly downloads. As such, ajv-keywords popularity was classified as popular.
We found that ajv-keywords demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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