What is ajv?
The ajv npm package is a fast JSON Schema validator that allows you to validate JSON data against a JSON schema. It supports the latest JSON Schema draft-07 and has several extensions. It can be used for data validation, data sanitization, and to ensure that JSON documents comply with a predefined schema.
What are ajv's main functionalities?
Validate data against a JSON Schema
This feature allows you to compile a JSON Schema and use it to validate JSON data. If the data does not conform to the schema, the errors can be logged or handled as needed.
{"const Ajv = require('ajv');
const ajv = new Ajv();
const schema = {
"type": "object",
"properties": {
"foo": {"type": "integer"},
"bar": {"type": "string"}
},
"required": ["foo"]
};
const validate = ajv.compile(schema);
const valid = validate({foo: 1, bar: 'abc'});
if (!valid) console.log(validate.errors);"}
Add custom keywords
Ajv allows you to define custom keywords for a JSON Schema, which can be used to create custom validation rules that are not defined in the JSON Schema specification.
{"const Ajv = require('ajv');
const ajv = new Ajv();
ajv.addKeyword('even', {
validate: function(schema, data) {
return data % 2 === 0;
}
});
const schema = {"even": true};
const validate = ajv.compile(schema);
const valid = validate(2); // true
const invalid = validate(3); // false"}
Asynchronous validation
Ajv supports asynchronous schema compilation, which is useful when your JSON Schema depends on other schemas that need to be fetched remotely.
{"const Ajv = require('ajv');
const ajv = new Ajv({loadSchema: loadExternalSchema});
// Assume loadExternalSchema is a function that loads a schema asynchronously
ajv.compileAsync(schema).then(function(validate) {
const valid = validate(data);
if (!valid) console.log(validate.errors);
}).catch(function(err) {
console.error('Failed to compile schema:', err);
});"}
Other packages similar to ajv
joi
Joi is a powerful schema description language and data validator for JavaScript. Unlike ajv, which focuses on JSON Schema, Joi allows you to create validation schemas using a fluent API. It is often used for validating data in REST APIs.
tv4
Tiny Validator (tv4) is a small and fast JSON Schema (v4) validator. It is less feature-rich compared to ajv and does not support the latest JSON Schema specifications, but it is suitable for simple validation tasks.
jsonschema
The jsonschema package is another validator for JSON Schema that supports draft-04/06/07. It is not as fast as ajv but provides a straightforward API for validating JSON data against schemas.
ajv - Another JSON schema Validator
One of the fastest JSON schema validators. It uses doT templates to generate super-fast validating functions.
JSON-schema standard
ajv implements full JSON-schema draft 4 standard:
- all validation keywords
- full support of remote refs (remote schemas have to be pre-loaded)
- correct string lengths for strings with unicode pairs (can be turned off)
- formats defined by JSON-schema (can be turned off)
ajv passes all the tests from JSON Schema Test Suite (apart from the one that requires that 1.0
is not an integer).
TODO
- resolve missing remote refs when schemas are added
- custom formats (via options)
- schema validation before compilation
- bundle compiled templates (doT will be dev dependency)
Install
npm install ajv
Usage
var ajv = require('ajv')(options);
var validate = ajv.compile(schema);
var valid = validate(data);
if (!valid) console.log(validate.errors);
or
// ...
var valid = ajv.validate(schema, data);
// ...
ajv compiles schemas to functions and caches them in both cases (using stringified schema as a key - using json-stable-stringify), so that the next time the same schema is used (not necessarily the same object instance) it won't be compiled again.
Options
- allErrors: check all rules collecting all errors. Default is to return after the first error.
- verbose: include the reference to the part of the schema and validated data in errors (false by default).
- format: validate formats (true by default).
- meta: add meta-schema so it can be used by other schemas (true by default).
- uniqueItems: validate
uniqueItems
(true by default). - unicode: calculate correct length of strings with unicode pairs (true by default). Pass
false
to use .length
of strings that is faster, but gives "incorrect" lengths of strings with unicode pairs - each unicode pair is counted as two characters. - beautify: format the generated function with js-beautify (the validating function is generated without line-breaks).
npm install js-beautify
to use this option. true
or js-beautify options can be passed.
Tests
git submodule update --init
npm test