io-ts-schema

Convert io-ts types to JSON schema

Installation

npm install io-ts-schema

Usage

import * as t from 'io-ts';
import * as i from 'io-ts-schema';
 
const type = t.strict({
  name: t.union([t.string, t.undefined]),
  rank: i.string('One parameter is a description'),
  quote: i.string({
    description: 'Object for more fields',
    minLength: 5,
    maxLenth: 10,
    pattern: 'w+',
  }),
  coordinates: t.array(t.number),
  tags: t.readonlyArray(t.string),
  status: t.keyof({
    on: null,
    off: null,
    idle: null,
  }),
  age: t.union([t.Int, t.string]),
  admin: t.boolean,
  links: t.type({
    facebook: t.string,
    twitter: t.string,
  }),
});
 
const json = convert(type);
/*
{
    type: 'object',
    required: ['coordinates', 'tags', 'status', 'age', 'admin', 'links', 'rank', 'quote'],
    additionalProperties: false,
    properties: {
      name: { type: 'string' },
      rank: { type: 'string', description: 'One parameter is a description' },
      quote: { 
        type: 'string', 
        description: 'Object for more fields',
        minLength: 5,
        maxLenth: 10,
        pattern: '\w+
      },
      status: {
        type: 'string',
        enum: ['on', 'off', 'idle']
      },
      coordinates: {
        type: 'array',
        items: { type: 'number' }
      },
      tags: {
        type: 'array',
        items: { type: 'string' }
      },
      age: {
        oneOf: [{ type: 'integer' }, { type: 'string' }]
      },
      admin: { type: 'boolean' },
      links: {
        type: 'object',
        required: ['facebook', 'twitter'],
        properties: {
          facebook: { type: 'string' },
          twitter: { type: 'string' }
        }
      }
    }
  }
*/

Why?

You could take your types and use them on Fastify for validation. This is useful if you have already iots types in your system and/or don't want to have a build step to generate interfaces from the JSON schemas.

Notes

• t.Function, t.Void and t.Undefined will be ignored, but t.Undefined will be used if its in a t.union to mark object properties as not required.

Limitations

It won't work with custom types, and will work with branded types, but only will take the base type (with the exception of t.Int).

You can only add objects in intersections (t.partial, t.type and t.strict will work). Nested intersections are fine as long as its objects all the way down. It will throw with a TypeError if not.