idrise / genson-js

JSON Schema Generator

genson-js

genson-js is a user-friendly JSON Schema generator built in TypeScript/JavaScript.

This is not the JavaScript equivalent of the Java Genson library. The motivation for this library was to port GenSON python library to JS, however having exactly the same api or possiblities was not a goal.

genson-js's core function is to take JSON objects and generate schemas that describe them, with an ability to merge schemas.

Usage

Creating schemas

To infer a schema from existing object:

import { createSchema } from 'genson-js';

const schema = createSchema({
    userName: 'smith',
    languages: ['c++', 'java'],
    age: 40,
});

The following schema will be created:

{
  type: "object",
  properties: {
    userName: {
      type: "string",
    },
    languages: {
      type: "array",
      items: {
        type: "string",
      },
    },
    age: {
      type: "integer",
    },
  },
  required: ["userName", "languages", "age"],
};

Merging schemas

You can merge 2 or more schemas, so that merged schema would be kind of a superset of the schemas that it was built from:

import { mergeSchemas } from 'genson-js';

const merged = mergeSchemas([{ type: ValueType.Number }, { type: ValueType.String }]);

// will create merged schema like this:
// { type: ['number', 'string'] }

Create compound schema

Shorthand for createSchema + mergeSchemas.
Can take multiple inputs and create one compound schema:

import { createCompoundSchema } from 'genson-js';

const schema = createCompoundSchema([{ age: 19, name: 'John' }, { age: 23, admin: true }, { age: 35 }]);

// Will create the following schema:
// {
//   type: 'object',
//   properties: { admin: { type: 'boolean' }, age: { type: 'integer' }, name: { type: 'string' } },
//   required: ['age']
// }

Exending schemas

You can extend existing schema to match some value:

import { extendSchema } from 'genson-js';

const extended = extendSchema({ type: ValueType.Number }, 'some string');

// will create extended schema like this:
// { type: ['number', 'string'] }

Comparing schemas

You can compare 2 schemas for equality like this:

import { areSchemasEqual } from 'genson-js';

areSchemasEqual({ type: ValueType.Number }, { type: ValueType.Number });
// will return true

Subset

You can also check if one schema is a subset of another one like so:

import { isSubset } from 'genson-js';

isSubset(
    { type: ValueType.Array, items: { type: [ValueType.Boolean, ValueType.Integer] } },
    { type: ValueType.Array, items: { type: [ValueType.Boolean] } }
);
// will return true

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You can find more examples in the unit tests.