json-schema-faker: A JavaScript repository from alockwood05

Use JSON Schema along with fake generators to provide consistent fake data for your system. Note that json-schema-faker supports (currently) the JSON-Schema specification draft-04 only.

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Basics
Advanced
Misc

Online demo

See online demo.

Install

Install json-schema-faker with npm:

npm install json-schema-faker --save-dev

Overview

JSON-schema-faker (or jsf for short) combines two things:

The JSON-schema specification, that defines what is the allowed content of a JSON document
Fake data generators, that are used to generate basic or complex data, conforming to the schema. Following libraries come bundled with jsf:

Example usage

var jsf = require('json-schema-faker');

var schema = {
  type: 'object',
  properties: {
    user: {
      type: 'object',
      properties: {
        id: {
          $ref: '#/definitions/positiveInt'
        },
        name: {
          type: 'string',
          faker: 'name.findName'
        },
        email: {
          type: 'string',
          format: 'email',
          faker: 'internet.email'
        }
      },
      required: ['id', 'name', 'email']
    }
  },
  required: ['user'],
  definitions: {
    positiveInt: {
      type: 'integer',
      minimum: 0,
      exclusiveMinimum: true
    }
  }
};

var sample = jsf(schema);

console.log(sample.user.name);
// output: John Doe

Gist demos

Clone these gists and execute them locally (each gist has its own readme with instructions):

jsf console - minimal example of jsf working directly under command line
jsf grunt - example of jsf working under grunt.js

Supported keywords

$ref — Resolve internal references only, and/or external if provided.
required — All required properties are guaranteed, if not can be omitted.
pattern — Generate samples based on RegExp values.
format — Core formats only: date-time, email, hostname, ipv4, ipv6 and uri.
enum — Returns any of these enumerated values.
minLength/maxLength — Applies length constraints to string values.
minimum/maximum — Applies constraints to numeric values.
exclusiveMinimum/exclusiveMaximum — Adds exclusivity for numeric values.
multipleOf — Multiply constraints for numeric values.
items — Support for subschema and fixed item values.
minItems/maxItems — Adds length constraints for array items.
uniqueItems — Applies uniqueness constraints for array items.
additionalItems — Partially supported (?)
allOf/oneOf/anyOf — Subschema combinators.
properties — Object properties to be generated.
minProperties/maxProperties — Adds length constraints for object properties.
patternProperties — RegExp-based object properties.
additionalProperties — Partially supported (?)
dependencies — Not supported yet (?)
not — Not supported yet (?)

Using references

Inline references are fully supported (json-pointers) but external can't be resolved by json-schema-faker.

In order to achieve that you can use refaker and then use the resolved schemas:

var schema = {
  type: 'object',
  properties: {
    someValue: {
      $ref: 'otherSchema'
    }
  }
};

var refs = [
  {
    id: 'otherSchema',
    type: 'string'
  }
];

var sample = jsf(schema, refs);

console.log(sample.someValue);
// output: voluptatem

Faking values

json-schema-faker has built-in generators for core-formats, Faker.js and Chance.js are also supported.

You can use faker or chance properties but they are optional:

{
  "type": "string",
  "faker": "internet.email"
}

The above schema will invoke:

require('faker').internet.email();

Another example is passing arguments to the generator:

{
  "type": "string",
  "chance": {
    "email": {
      "domain": "fake.com"
    }
  }
}

And will invoke:

var Chance = require('chance'),
  chance = new Chance();

chance.email({ "domain": "fake.com" });

If you pass an array, they will be used as raw arguments.

Note that both generators has higher precedence than format.

You can also use standard JSON Schema keywords, e.g. pattern:

{
  "type": "string",
  "pattern": "yes|no|maybe|i don't know"
}

Custom formats

Additionally, you can add custom generators for those:

jsf.formats('semver', function(gen, schema) {
  return gen.randexp('^\\d\\.\\d\\.\\d{1,2}$');
});

Now that format can be generated:

{
  "type": "string",
  "format": "semver"
}

Usage:

formats() — Return all registered formats (custom only)
formats(obj) — Register formats by key/value → name/callback
formats(name) — Returns that format generator (undefined if not exists)
formats(name, callback) — Register a custom format by name/callback

Callback:

gen (object) — Built in generators
- faker (object) — Faker.js instance
- chance (object) — Chance.js instance
- randexp (function) — Randexp generator
schema (object) — The schema for input

Note that custom generators has lower precedence than core ones.

Extending dependencies

You may extend Faker.js:

var jsf = require('json-schema-faker');

jsf.extend('faker', function(faker){
  faker.locale = "de"; // or any other language
  faker.custom = {
    statement: function(length) {
      return faker.name.firstName() + " has " + faker.finance.amount() + " on " + faker.finance.account(length) + ".";
    }
  };
  return faker;
});

var schema = {
  "type": "string",
  "faker": {
    "custom.statement": [19]
  }
}

var sample = jsf(schema);

or if you want to use faker's individual localization packages, simply do the following:

jsf.extend('faker', function() {
  // just ignore the passed faker instance
  var faker = require('faker/locale/de');
  // do other stuff
  return faker;
});

You can also extend Chance.js, using built-in chance.mixin function:

var jsf = require('json-schema-faker');

jsf.extend('chance', function(chance){
  chance.mixin({
    'user': function() {
      return {
        first: chance.first(),
        last: chance.last(),
        email: chance.email()
      };
    }
  });

  return chance;
});

var schema = {
  "type": "string",
  "chance": "user"
}

var sample = jsf(schema);

The first parameter of extend function is the generator name (faker or chance). The second one is the function that accepts the dependency library; the function alters the library and returns it.

Inferred Types

JSON Schema does not require you to provide the type property for your JSON Schema documents and document fragments.

But since jsf uses the type property to create the proper fake data, we attempt to infer the type whenever it is not provided. We do this based on the JSON Schema validation properties you use.

Now this means that if you do not use any of the JSON Schema validation properties, json-schema-faker will not be able to infer the type for you and you will need to explicitly set your type manually.)

Below is the list of JSON Schema validation properties and the inferred type based on the property:

array

additionalItems
items
maxItems
minItems
uniqueItems

integer (Number uses the same properties so if you need number, set your type explicitly)

exclusiveMaximum
exclusiveMinimum
maximum
minimum
multipleOf

object

additionalProperties
dependencies
maxProperties
minProperties
patternProperties
properties
required

string

maxLength
minLength
pattern

Automation

Grunt plugin

Use grunt-jsonschema-faker to automate running json-schema-faker against your JSON schemas.

Resources

JSON, JSON Schema & JSON-schema-faker - WarsawJS meetup presentation recording, a step-by-step guide to JSON-related tools, including jsf

Motivation

There were some existing projects or services trying to achieve similar goals as jsf:

but they were either incomplete, outdated, broken or non-standard. That's why jsf was created.

Contribution

Any contribution is well received, please see contribution guide.

alockwood05/json-schema-faker

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