json-schema-validator-generator

A Flow type and JS validator code generator for JSON Schema.

Install

yarn add json-schema-validator-generator

Usage

Basic

import generate from 'json-schema-validator-generator';
const schema = {type: 'string'};
const {flow, js} = generate(schema);

console.log(flow);
// declare type root = string;

console.log(js);
// (function() {
//   function f0(v0) {
//     if (typeof v0 !== 'string') {
//       return 1;
//     }
//     return 0;
//   }
//   return {
//     root: f0,
//   };
// })()

Flow Output

The generated flow string is meant for direct consumption in a project's library definitions. See scripts/generate.js for an example script which writes flow types to src/decls/json-schema.js.

JS Output

The generated JS string is an IIFE that evaluates to an object whose values are validator functions. Each validator returns a number with 0 representing a valid model and a nonzero number otherwise.

type Validator = (data: mixed) => number;

It's recommended to write the generated JS to the filesystem, but it's possible to use the generated code at runtime.

Static JS Usage

See scripts/generate.js for an example script which writes validators to src/generated-validator.js.

Dynamic JS Usage (not recommended)

import generate from 'json-schema-validator-generator';

const validatorForSchema = (schema) => {
  const {js} = generate(schema);
  return eval(js);
};

Advanced

Sometimes we may be using JSON Schema to define a collection of types. In this case, the generator needs some information about the subschema to be generated.

For example, consider the definition of a binary tree of numbers:

import generate from 'json-schema-validator-generator';
const schema = {
  definitions: {
    node: {
      type: 'object',
      properties: {
        left: {$ref: '#/definitions/nodeOrValue'},
        right: {$ref: '#/definitions/nodeOrValue'},
      },
      required: ['left', 'right'],
    },
    nodeOrValue: {
      oneOf: [
        {$ref: '#/definitions/node'},
        {type: 'number'},
      ],
    },
  },
};
const {flow, js} = generate(schema, {node: schema.definitions.node});
const nodeValidator = eval(js).node;

console.log(nodeValidator({left: 1, right: 2})); // 0
console.log(nodeValidator({left: 1, right: {left: 2, right: 3}})); // 0

console.log(nodeValidator(1)); // error
console.log(nodeValidator({left: 1})); // error
console.log(nodeValidator({left: 1, right: '2'})); // error