fast-json-stringify  

fast-json-stringify is x1-5 times faster than JSON.stringify(). It is particularly suited if you are sending small JSON payloads, the advantages reduces on large payloads.

Benchmarks:

JSON.stringify array x 3,500 ops/sec ±0.91% (85 runs sampled)
fast-json-stringify array x 4,456 ops/sec ±1.68% (87 runs sampled)
JSON.stringify long string x 13,395 ops/sec ±0.88% (91 runs sampled)
fast-json-stringify long string x 95,488 ops/sec ±1.04% (90 runs sampled)
JSON.stringify short string x 5,059,316 ops/sec ±0.86% (92 runs sampled)
fast-json-stringify short string x 12,219,967 ops/sec ±1.16% (91 runs sampled)
JSON.stringify obj x 1,763,980 ops/sec ±1.30% (88 runs sampled)
fast-json-stringify obj x 5,085,148 ops/sec ±1.56% (89 runs sampled)

Table of contents:

• Example
• API
• fastJsonStringify
• Specific use cases
• Required
• Missing fields
• Pattern Properties
• Additional Properties
• Reuse - $ref
• Acknowledgements
• License

Example

const fastJson = require('fast-json-stringify')
const stringify = fastJson({
  title: 'Example Schema',
  type: 'object',
  properties: {
    firstName: {
      type: 'string'
    },
    lastName: {
      type: 'string'
    },
    age: {
      description: 'Age in years',
      type: 'integer'
    },
    reg: {
      type: 'string'
    }
  }
})

console.log(stringify({
  firstName: 'Matteo',
  lastName: 'Collina',
  age: 32,
  reg: /"([^"]|\\")*"/
}))

API

fastJsonStringify(schema)

Build a stringify() function based on jsonschema.

Supported types:

• 'string'
• 'integer'
• 'number'
• 'array'
• 'object'
• 'boolean'
• 'null'

And nested ones, too.

Specific use cases

Required

You can set specific fields of an object as required in your schema, by adding the field name inside the required array in your schema.
Example:

const schema = {
  title: 'Example Schema with required field',
  type: 'object',
  properties: {
    nickname: {
      type: 'string'
    },
    mail: {
      type: 'string'
    }
  },
  required: ['mail']
}

If the object to stringify has not the required field(s), fast-json-stringify will throw an error.

Missing fields

If a field is present in the schema (and is not required) but it is not present in the object to stringify, fast-json-stringify will not write it in the final string.
Example:

const stringify = fastJson({
  title: 'Example Schema',
  type: 'object',
  properties: {
    nickname: {
      type: 'string'
    },
    mail: {
      type: 'string'
    }
  }
})

const obj = {
  mail: 'mail@example.com'
}

console.log(stringify(obj)) // '{"mail":"mail@example.com"}'

Pattern properties

fast-json-stringify supports pattern properties as defined inside JSON schema.
patternProperties must be an object, where the key is a valid regex and the value is an object, declared in this way: { type: 'type' }.
patternProperties will work only for the properties that are not explicitly listed in the properties object.
Example:

const stringify = fastJson({
  title: 'Example Schema',
  type: 'object',
  properties: {
    nickname: {
      type: 'string'
    }
  },
  patternProperties: {
    'num': {
      type: 'number'
    },
    '.*foo$': {
      type: 'string'
    }
  }
})

const obj = {
  nickname: 'nick',
  matchfoo: 42,
  otherfoo: 'str'
  matchnum: 3
}

console.log(stringify(obj)) // '{"matchfoo":"42","otherfoo":"str","matchnum":3,"nickname":"nick"}'

Additional properties

fast-json-stringify supports additional properties as defined inside JSON schema.
additionalProperties must be an object or a boolean, declared in this way: { type: 'type' }.
additionalProperties will work only for the properties that are not explicitly listed in the properties and patternProperties objects.

If additionalProperties is not present or is setted to false, every property that is not explicitly listed in the properties and patternProperties objects, will be ignored, as said in Missing fields.
If additionalProperties is setted to true, it will be used fast-safe-stringify to stringify the additional properties. If you want to achieve maximum performances we strongly encourage you to use a fixed schema where possible.
Example:

const stringify = fastJson({
  title: 'Example Schema',
  type: 'object',
  properties: {
    nickname: {
      type: 'string'
    }
  },
  patternProperties: {
    'num': {
      type: 'number'
    },
    '.*foo$': {
      type: 'string'
    }
  },
  additionalProperties: {
    type: 'string'
  }
})

const obj = {
  nickname: 'nick',
  matchfoo: 42,
  otherfoo: 'str'
  matchnum: 3,
  nomatchstr: 'valar morghulis',
  nomatchint: 313
}

console.log(stringify(obj)) // '{"matchfoo":"42","otherfoo":"str","matchnum":3,"nomatchstr":"valar morghulis",nomatchint:"313","nickname":"nick"}'

Reuse - $ref

If you want to reuse a definition of a value, you can use the property $ref.
The value of $ref must be a string in JSON Pointer format.
Example:

const schema = {
  title: 'Example Schema',
  definitions: {
    num: {
      type: 'object',
      properties: {
        int: {
          type: 'integer'
        }
      }
    },
    str: {
      type: 'string'
    }
  },
  type: 'object',
  properties: {
    nickname: {
      $ref: '#/definitions/str'
    }
  },
  patternProperties: {
    'num': {
      $ref: '#/definitions/num'
    }
  },
  additionalProperties: {
    $ref: '#/definitions/def'
  }
}

const stringify = fastJson(schema)

If you need to use an external definition, you can pass it as an option to fast-json-stringify.
Example:

const schema = {
  title: 'Example Schema',
  type: 'object',
  properties: {
    nickname: {
      $ref: 'strings#/definitions/str'
    }
  },
  patternProperties: {
    'num': {
      $ref: 'numbers#/definitions/num'
    }
  },
  additionalProperties: {
    $ref: 'strings#/definitions/def'
  }
}

const externalSchema = {
  numbers: {
    definitions: {
      num: {
        type: 'object',
        properties: {
          int: {
            type: 'integer'
          }
        }
      }
    }
  },
  strings: require('./string-def.json')
}

const stringify = fastJson(schema, { schema: externalSchema })

Acknowledgements

This project was kindly sponsored by nearForm.

License

MIT