Tiny Validator (for v4 JSON Schema)

⚠️ This project is no longer actively maintained.

Use json-schema draft v4 to validate simple values and complex objects using a rich validation vocabulary (examples).

There is support for $ref with JSON Pointer fragment paths (other-schema.json#/properties/myKey).

Usage 1: Simple validation

var valid = tv4.validate(data, schema);

If validation returns false, then an explanation of why validation failed can be found in tv4.error.

The error object will look something like:

{
    "code": 0,
    "message": "Invalid type: string",
    "dataPath": "/intKey",
    "schemaPath": "/properties/intKey/type"
}

The "code" property will refer to one of the values in tv4.errorCodes - in this case, tv4.errorCodes.INVALID_TYPE.

To enable external schema to be referenced, you use:

tv4.addSchema(url, schema);

If schemas are referenced ($ref) but not known, then validation will return true and the missing schema(s) will be listed in tv4.missing. For more info see the API documentation below.

Usage 2: Multi-threaded validation

Storing the error and missing schemas does not work well in multi-threaded environments, so there is an alternative syntax:

var result = tv4.validateResult(data, schema);

The result will look something like:

{
    "valid": false,
    "error": {...},
    "missing": [...]
}

Usage 3: Multiple errors

Normally, tv4 stops when it encounters the first validation error. However, you can collect an array of validation errors using:

var result = tv4.validateMultiple(data, schema);

The result will look something like:

{
    "valid": false,
    "errors": [
        {...},
        ...
    ],
    "missing": [...]
}

Asynchronous validation

Support for asynchronous validation (where missing schemas are fetched) can be added by including an extra JavaScript file. Currently, the only version requires jQuery (tv4.async-jquery.js), but the code is very short and should be fairly easy to modify for other libraries (such as MooTools).

Usage:

tv4.validate(data, schema, function (isValid, validationError) { ... });

validationError is simply taken from tv4.error.

Cyclical JavaScript objects

While they don't occur in proper JSON, JavaScript does support self-referencing objects. Any of the above calls support an optional third argument: checkRecursive. If true, tv4 will handle self-referencing objects properly - this slows down validation slightly, but that's better than a hanging script.

Consider this data, notice how both a and b refer to each other:

var a = {};
var b = { a: a };
a.b = b;
var aSchema = { properties: { b: { $ref: 'bSchema' }}};
var bSchema = { properties: { a: { $ref: 'aSchema' }}};
tv4.addSchema('aSchema', aSchema);
tv4.addSchema('bSchema', bSchema);

If the checkRecursive argument were missing, this would throw a "too much recursion" error.

To enable support for this, pass true as additional argument to any of the regular validation methods:

tv4.validate(a, aSchema, true);
tv4.validateResult(data, aSchema, true);
tv4.validateMultiple(data, aSchema, true);

The banUnknownProperties flag

Sometimes, it is desirable to flag all unknown properties as an error. This is especially useful during development, to catch typos and the like, even when extra custom-defined properties are allowed.

As such, tv4 implements "ban unknown properties" mode, enabled by a fourth-argument flag:

tv4.validate(data, schema, checkRecursive, true);
tv4.validateResult(data, schema, checkRecursive, true);
tv4.validateMultiple(data, schema, checkRecursive, true);

API

There are additional api commands available for more complex use-cases:

addSchema(uri, schema)

Pre-register a schema for reference by other schema and synchronous validation.

tv4.addSchema('http://example.com/schema', { ... });

• uri the uri to identify this schema.
• schema the schema object.

Schemas that have their id property set can be added directly.

tv4.addSchema({ ... });

getSchema(uri)

Return a schema from the cache.

• uri the uri of the schema (may contain a # fragment)

var schema = tv4.getSchema('http://example.com/schema');

getSchemaMap()

Return a shallow copy of the schema cache, mapping schema document URIs to schema objects.

var map = tv4.getSchemaMap();

var schema = map[uri];

getSchemaUris(filter)

Return an Array with known schema document URIs.

• filter optional RegExp to filter URIs

var arr = tv4.getSchemaUris();

// optional filter using a RegExp
var arr = tv4.getSchemaUris(/^https?://example.com/);

getMissingUris(filter)

Return an Array with schema document URIs that are used as $ref in known schemas but which currently have no associated schema data.

Use this in combination with tv4.addSchema(uri, schema) to preload the cache for complete synchronous validation with.

• filter optional RegExp to filter URIs

var arr = tv4.getMissingUris();

// optional filter using a RegExp
var arr = tv4.getMissingUris(/^https?://example.com/);

dropSchemas()

Drop all known schema document URIs from the cache.

tv4.dropSchemas();

freshApi()

Return a new tv4 instance with no shared state.

var otherTV4 = tv4.freshApi();

reset()

Manually reset validation status from the simple tv4.validate(data, schema). Although tv4 will self reset on each validation there are some implementation scenarios where this is useful.

tv4.reset();

setErrorReporter(reporter)

Sets a custom error reporter. This is a function that accepts three arguments, and returns an error message (string):

tv4.setErrorReporter(function (error, data, schema) {
    return "Error code: " + error.code;
});

The error object already has everything aside from the .message property filled in (so you can use error.params, error.dataPath, error.schemaPath etc.).

If nothing is returned (or the empty string), then it falls back to the default error reporter. To remove a custom error reporter, call tv4.setErrorReporter(null).

language(code)

Sets the language used by the default error reporter.

• code is a language code, like 'en' or 'en-gb'

tv4.language('en-gb');

If you specify a multi-level language code (e.g. fr-CH), then it will fall back to the generic version (fr) if needed.

addLanguage(code, map)

Add a new template-based language map for the default error reporter (used by tv4.language(code))

• code is new language code
• map is an object mapping error IDs or constant names (e.g. 103 or "NUMBER_MAXIMUM") to language strings.

tv4.addLanguage('fr', { ... });

// select for use
tv4.language('fr')

If you register a multi-level language code (e.g. fr-FR), then it will also be registered for plain fr if that does not already exist.

addFormat(format, validationFunction)

Add a custom format validator. (There are no built-in format validators. Several common ones can be found here though)

• format is a string, corresponding to the "format" value in schemas.
• validationFunction is a function that either returns:
  • null (meaning no error)
  • an error string (explaining the reason for failure)

tv4.addFormat('decimal-digits', function (data, schema) {
	if (typeof data === 'string' && !/^[0-9]+$/.test(data)) {
		return null;
	}
	return "must be string of decimal digits";
});

Alternatively, multiple formats can be added at the same time using an object:

tv4.addFormat({
	'my-format': function () {...},
	'other-format': function () {...}
});

defineKeyword(keyword, validationFunction)

Add a custom keyword validator.

• keyword is a string, corresponding to a schema keyword
• validationFunction is a function that either returns:
  • null (meaning no error)
  • an error string (explaining the reason for failure)
  • an error object (containing some of: code/message/dataPath/schemaPath)

tv4.defineKeyword('my-custom-keyword', function (data, value, schema) {
	if (simpleFailure()) {
		return "Failure";
	} else if (detailedFailure()) {
		return {code: tv4.errorCodes.MY_CUSTOM_CODE, message: {param1: 'a', param2: 'b'}};
	} else {
		return null;
	}
});

schema is the schema upon which the keyword is defined. In the above example, value === schema['my-custom-keyword'].

If an object is returned from the custom validator, and its message is a string, then that is used as the message result. If message is an object, then that is used to populate the (localisable) error template.

defineError(codeName, codeNumber, defaultMessage)

Defines a custom error code.

• codeName is a string, all-caps underscore separated, e.g. "MY_CUSTOM_ERROR"
• codeNumber is an integer > 10000, which will be stored in tv4.errorCodes (e.g. tv4.errorCodes.MY_CUSTOM_ERROR)
• defaultMessage is an error message template to use (assuming translations have not been provided for this code)

An example of defaultMessage might be: `"Incorrect moon (expected {