json-schema-validate

Validate JSON against a JSON-Schema

This project uses ajv, ajv-formats, and json-source-map to validate a JSON object and provide error messages with line, column, and pos information.

I've also implemented a hack to add a banUnknownProperties feature.

Command Line Usage

git clone [email protected]:pbatey/json-schema-validate.git
cd json-schema-validate
npm install
npm run cli example.json example.schema.json

Example Output

$ npm run cli example.json example.schema.json

> [email protected] cli /Users/pbatey200/src/github.com/pbatey/json-schema-validate
> node --es-module-specifier-resolution=node cli.js "example.json" "example.schema.json"

🍻 example.json is valid but has unknown properties
[
  {
    "keyword": "additionalProperties",
    "dataPath": "",
    "schemaPath": "#/additionalProperties",
    "params": {
      "additionalProperty": "timestamp"
    },
    "message": "should NOT have additional properties",
    "pointer": {
      "value": {
        "line": 0,
        "column": 0,
        "pos": 0
      },
      "valueEnd": {
        "line": 9,
        "column": 1,
        "pos": 322
      }
    }
  }
]

Install as an npm dependancy

I thought about publishing this as an npm package, but there's already a bunch of packages for json schema validation. I didn't want to add to the confusion, and one is already named json-schema-validate -- I didn't have it in me to come up with another name right now.

Let me know if you think I should reconsider. I'd appreciate any name suggestions.

npm i git+ssh://[email protected]:pbatey/json-schema-validate.git#semver:^1.0

Using the API

This is an example of using the API from Node.js -- I believe it'll work in a browser since ajv and json-source-map do, but haven't tried it.

import validate from 'json-schema-validate'
import fs from 'fs'

const jsonText = fs.readFileAsync('./example.json').toString()
const jsonSchema = JSON.parse(fs.readFileAsync('./example.schema.json').toString())

const banUnknownProperties = true
const errors = validate(jsonText, jsonSchema, banUnknownProperties)

Specifying Ajv Options

The Ajv instance created in validate.js specifies no options. In order to specify options, or add multiple schemas, specify an Ajv instance.

import Ajv from 'ajv/dist/2019'
import ajvFormats from 'ajv-formats'
import validate from 'json-schema-validate'

const ajvOptions = { allErrors: true }
const ajv = new Ajv.default(ajvOptions) // constructor weirdness
ajvFormats(ajv)

... read jsonTexta and jsonSchema ...

validate(jsonText, jsonSchema)

Note: I ran into weirdness with the Ajv constructor using Node.js and the --es-module-specifier-resolution=node flag. Had to use new Ajv.default() to construct an instance. Your mileage may vary.

API Documentation

validate(json, schema, strict, ajv)

Validates JSON against a JSON-Schema, appending pointer information (line, column, pos) to returned errors if json is provided as a string.

defined in validate.js

Parameters	Name	Description
{string|object}	json	JSON to validate. A string will be parsed as JSON.
{object}	schema	A JSON-Schema
{boolean}	strict	If set, schema will be adjusted to ban unknown properties
{boolean}	strict	Optional. An Ajv instance. Will use a vanilla instance w/ ajvformat if not provided.

Returns	Description
{array|null}	An array of Ajv errors decorated with a pointer field from json-source-map

banUnknownProperties(schema)

Forces additionalProperties to false within a JSON-Schema definition.

Returns a shallow copy of the schema with shallow copy of nodes that have been modified so that the original schema value is unchanged, but this should not be used as a deep-copy.

defined in banUnknownProperties.js

Parameters	Name	Description
{object}	schema	A JSON-Schema

Returns	Description
{object}	An adjusted version of the schema that sets additionalProperties to false