fn-validator

Extendable and Isomorphic functional schema validator for browser and Node.js

Motivation

JavaScript being dynamic and weakly typed language, does not support anything which can help you validate the JSON object structure.

However, writing business logic in NodeJS, or even writing a browser based application requires strong type object contract interface to validate the data coming from or going to external sources and acknowledge the error messages in case of mismatch. Now there are some JSON schema standards and libraries out there which help you do that but they lack the extensibility in terms of defining new kind of validators or composing them to make hybrid validators.

This library aims at

1. Defining flexible and tiny architecture to plug in any kind of reusable custom validator.

2. Using JavaScript as functional language without side effects. All validators are pure functions.

3. Providing facility to compose different kind of validators along with custom error messages.

4. Being predictable with full test coverage.

Install

npm install fn-validator --save

Use

var v = require("fn-validator");

var userSchema = v.object({
   firstName : v.string,
   lastName : v.all([v.string, v.minLength(2), v.maxLength(30)]),
   gender : v.enum(["Male", "Female", "Other"]),
   age : v.number,
   height : v.between(160, 190),
   graduationDate : v.before(new Date("2000-01-01")),
   single : v.boolean,
   hasGirlfriend : v.optional(v.boolean)
 })

 var schema = v.object({
     orgName : v.string
     users : v.arrayOf(userSchema)
 })

var isValid = v.validate(schema, objectToBeValidated);

if(!Object.isEmpty(result))
  //handle error
else
  // all good

Custom Validator

If there is an error, Return String value which is a error message

Return true or don't return anything at all if value is valid

Define Validator

function customValidator(key, value, object) {
  var errorMessageString = "Value is not valid";
  if(value is not valid) {
    return errorMessageString;
  }
//  else
//    return true;
}

Define schema

var schema = object({
  attribute: customValidator
})

Validate

expect(v.validate(schema, objectToBeValidated)).toEqual({
  error_attribute : "Value is not valid"
})