ajv

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);
});"}