json-schema-visitor

A package for inspecting JSON schemas.

Supported schema types

These directly translate to the method names you need to supply to the configuration object passed to createVisitor:

• object
• array
• enum
• boolean
• number
• null
• string
• oneOf
• anyOf
• allOf
• ref
• unknown

Usage

Simple example

import createVisitor from 'json-schema-visitor'

const visitor = createVisitor({
  object(schema) {
    return `An object schema: ${JSON.stringify(schema)}`
  }
  array(schema) {
    return `An array schema: ${JSON.stringify(schema)}`
  }
})

// 2 cases handled
expect(visitor({ type: 'object' })).toBe('An object schema: {type:"object"}')
expect(visitor({ type: 'array' })).toBe('An array schema: {type:"array"}')

// All other cases
expect(visitor({ type: 'string' })).toBeUndefined()
expect(visitor(null)).toBeUndefined()
expect(visitor('foo')).toBeUndefined()

Default visit method

You don't have to specify each visit method. You can have a fallback method named any which handles all unhandled cases.

const visitor = createVisitor({
  object(schema) {
    return 'An object schema'
  },
  any(schema) {
    return 'Everything else'
  }
})

// Case handled
expect(visitor({ type: 'object' })).toBe('An object schema')

// All other cases
expect(visitor({ type: 'string' })).toBe('Everything else')
expect(visitor(null)).toBe('Everything else')
expect(visitor('foo')).toBe('Everything else')

Extra arguments

You can pass extra arguments to the visitor. These arguments will be paseed as second, third, etc. arguments to each visit method.

const visitor = createVisitor({
  object(schema, someArg, otherArg) {
    return `An object schema. Also args: ${someArg} and ${otherArg}`
  }
})

expect(visitor({ type: 'object' }, 'foo', 42)).toBe('An object schema. Also args: foo and 42')

Recursive traversing

This visitor recursively visits every element of the schema, and applies a callback on them.

const visitor = createVisitor({
  object(schema, callback) {
    callback(schema)
    Object.keys(schema.properties)
      .map(key => schema.properties[key])
      .forEach(childSchema => visitor(childSchema, callback))
  }
  array(schema, callback) {
    callback(schema)
    visitor(schema.items, callback)
  },
  allOf(schema, callback) {
    callback(schema)
    schema.allOf.forEach(childSchema => visitor(childSchema, callback))
  },
  anyOf(schema, callback) {
    callback(schema)
    schema.anyOf.forEach(childSchema => visitor(childSchema, callback))
  },
  oneOf(schema, callback) {
    callback(schema)
    schema.oneOf.forEach(childSchema => visitor(childSchema, callback))
  }
  any(schema, callback) {
    callback(schema)
  }
})

visitor(someSchema, schema => console.log(schema))