Generate empty placeholder data from JSON Schemas

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220.1.58 years ago8 years agoMinified + gzip package size for empty-schema in KB


:crystalball: Generate empty placeholder data from JSON Schemas

Generating random data is useful for testing (try out JSON Schema Faker or hazy if you have this need), but developers often require empty placeholder data to work with, particularly when developing web forms.
The empty data that empty-schema generates conforms to the following: - Data is generated deterministically. If the schema is the same, the data will be the same. - Data is as simple as possible. - Data conforms to the form specified in the schema. It will, however, sometimes fail to be valid according to the schema. The reason for this is simple: you cannot generate all values automatically (see the rules section for more info on this).


npm install --save empty-schema


import {empty} from 'empty-schema'

const 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' ]


// {
//   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: empty-schema 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: empty-schema merges all schemas and works from that schema
to generate a value.
- enum: selects the first possible value. - $ref: just works!
Whenever specified, empty-schema uses the default value (even if it does not match the schema).


  • Lazy and greedy mode (aka "least" and "most")
  • Integrate deref, a more robust $ref library (has issues with Hyper-Schema)


This code is licensed under the ISC License