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Generate simple data that matches a json schema.

All libraries that generate data from a json-schema I could find generate random data that conforms to a json schema. This is nice for testing but is not well-suited for generating default data for forms for example.

json-schema-empty fills another niche. The data it generates conforms to the following qualities:

  • data is generated deterministically, if the schema is the same, the date will be the same.
  • the data is as simple as possible
  • the data conforms to the form specified in the schema. It will sometimes fail to be valid according to the schema however. The reason for this is simple: you cannot generate all values automatically (see the rules section for more info on this).


To install json-schema-empty, run:

npm install romeovs/json-schema-empty --save

The api is simple:

import empty from 'json-schema-empty';
var schema = {
  type: 'object'
, properties: {
    foo: {
      type: 'integer'
    , minimum: 12
    , multipleOf: 5
  , bar: {
      type: 'array'
    , items: { type: 'integer' }
    , minItems: 3
  , baz: {
      type: 'string'
      minLength: 5
, required: [ 'foo', 'bar', 'baz' ]
// logs:
// {
//   foo: 15,
//   bar: [ 0, 0, 0 ],
//   baz: ''
// }


  • string: because it impossible to guess what the string content should be, even when patterns and length limits are given, a string schema always results in the empty string: ''.

  • integer: json-schema-empty tries to satisfy the minimum, maximum and multipleOf constraints whenever possible wth the additional property that, when it is possible, 0 is returned.

  • number: just follows the integer schema.

  • object: tries to create a minimal object with as few keys as possible. Only keys that are in the required array are generated.

    Object size is ignored completely, for the same reason that the strings are empty: we cannot guess the keys.

  • array: when the item type is given, and minItems is given, the shortest array that matches this is generated. It also works when items is a tuple. maxItems is ignored. Whenever possible, the empty array is returned.

  • boolean: always results in false.

  • null: always results in null.

  • oneOf, anyOf: selects one of the accepted types and goes from there.

  • allOf: json-schema-empty merges all schemas and works from that schema to generate a value.

  • enum: selects the first possible value.

  • $ref: just works!

Whenever specified, json-schema-empty uses the default value (even if it does not match the schema).


This code is licensed under the ISC license




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