node package manager
Share your code. npm Orgs help your team discover, share, and reuse code. Create a free org ยป



The json-minus node module provides a tool for validating and preparing JavaScript objects for database insertion. It targets a subset of JSON documents called JSON Minus.


npm install json-minus


Create a JSON Minus validator by passing a property specification to the JSONMinus constructor:

var Person = JSONMinus({
    'name'         : {type: 'string', match: /[a-zA-Z]/},
    'eyeColor'     : {type: 'string', match: /^(blue|brown|green|gray|hazel)$/},
    'weight'       : {type: 'number', gt: 0, lt: 500},
    'likesSeafood' : {type: 'boolean'}

The resulting validator is a function that accepts an object and makes a validated copy of that object. Limited type conversion is performed as the input object is copied:

Person({name: 'Will', eyeColor: 'hazel', weight: '185'})


{name: 'Will', eyeColor: 'hazel', weight: 185, likesSeafood: false}

Nested Structures

A top-level property of a JSON Minus document may be an array of homogeneous objects. Such arrays and the properties of their contained sub-objects may be specified like this:

var Order = JSONMinus({
    'total'          : {type: 'string', match: /^\d+\.\d\d$/},
    'items.product'  : {type: 'string'},
    'items.price'    : {type: 'string', match: /^\d+\.\d\d$/},
    'items.quantity' : {type: 'integer', gte: 1}

In this example, an Order has the property items which contains an array of sub-objects. Each of those sub-objects have the properties product, price, and quantity.

Sub-objects may not contain further nested structures.

Type Conversion

JSON Minus object validators make deep copies of input objects as they perform validation. As the copy is made, some limited type conversion may take place.

Convesion to Strings

  • numbers that are finite and are not NaN will be converted to decimal strings
  • booleans will be converted to 'true' or 'false'
  • undefined will be converted to the empty string
  • all other non-string values will result in validation errors

Conversion to Numbers

  • strings representing finite decimal numbers will be converted to numbers
  • undefined will be converted to 0
  • all other non-numeric values will result in validation errors
  • Infinity, -Infinity, and NaN will result in validation errors

Conversion to Integers

Values will be converted to numbers using the rules specified above and then rounded to integers using Math.round().

Conversion to Booleans

  • the strings 'true' and '1' will be converted to true
  • the strings 'false', '0', and the empty string will be converted to false
  • the number 1 will be converted to true
  • the number 0 will be onverted to false
  • undefined will be converted to false
  • all other non-boolean values will result in validation errors

Validation Constraints

For Strings

String values may be constrained by a RegExp provided in the match property of the property specification. The match constraint is applied after type conversion.

For Numbers and Integers

Numbers and integers may be constrainted with a combination of the properties gt, gte, lt, and lte of the property specification. These constratins are applied after type conversion.

Omitting Empty Strings

There are some cases where you may prefer to completely omit a key from the validated copy if the value is an empty string. You can accomplish this with the omitEmpty option like this:

var CouchDoc = JSONMinus({
    _id:   {type: 'string', omitEmpty: true},
    _rev:  {type: 'string', omitEmpty: true},
    value: {type: 'string'}

Given the validator above,

CouchDoc({_id: 'abc', _rev: '', value: 'foo'})


{_id: 'abc', value: 'foo'}

The omitEmpty option is applied at the very end after the property is coerced to a string and validated via the match regular expression.


Will Conant,


The json-minus module is released under the MIT License.