schemaByExample – generate JSON schema from example object

index.js

import _ from 'lodash';


export default function schemaByExample(example) {
    if (_.isArray(example)) {
        return {
            type: 'array',
            items: schemaByExample(example[0])
        };
    } else if (_.isPlainObject(example)) {
        return {
            type: 'object',
            required: _.keys(example),
            properties: _.mapValues(example, schemaByExample)
        };
    } else if (_.isString(example)) {
        return {
            type: 'string'
        };
    } else if (_.isNumber(example)) {
        return {
            type: 'number'
        };
    } else if (_.isRegExp(example)) {
        return {
            type: 'string',
            pattern: example
        };
    } else if (_.isBoolean(example)) {
        return {
            type: 'boolean'
        };
    }

    return undefined;
};

test.js

import assert from 'assert';
import { validate } from 'jsonschema';
import schemaByExample from '.';


describe('schemaByExample', () => {
    it('produces a JSON schema that matches the given example object', () => {
        const example1 = {};
        const expectedSchema1 = { type: 'object', properties: {}, required: [] };
        const generatedSchema1 = schemaByExample(example1);

        assert.deepEqual(generatedSchema1, expectedSchema1);
        assert(validate(example1, generatedSchema1).valid);

        const example2 = { a: 5 };
        const expectedSchema2 = {
            type: 'object',
            required: ['a'],
            properties: {
                a: { type: 'number' }
            }
        };
        const generatedSchema2 = schemaByExample(example2);

        assert.deepEqual(generatedSchema2, expectedSchema2);
        assert(validate(example2, generatedSchema2).valid);

        const example3 = {
            response: {
                body: [{
                    customer: {}
                }]
            }
        };
        const expectedSchema3 = {
            type: 'object',
            required: ['response'],
            properties: {
                response: {
                    type: 'object',
                    required: ['body'],
                    properties: {
                        body: {
                            type: 'array',
                            items: {
                                type: 'object',
                                required: ['customer'],
                                properties: {
                                    customer: {
                                        type: 'object',
                                        required: [],
                                        properties: {}
                                    }
                                }
                            }
                        }
                    }
                }
            }
        };
        const generatedSchema3 = schemaByExample(example3);

        assert.deepEqual(generatedSchema3, expectedSchema3);
        assert(validate(example3, generatedSchema3).valid);
    });
});