F-Validator

Functional JSON validator

Features

• Minimal, ~200 LoC, no dependencies.
• Simple, validators are just functions, no special DSL to learn
• Powerful, compose basic/custom validators to build complex ones

Installation

npm install --save f-validator

Get started

const{ string, number, optional, or, objectOf, arrayOf, error }=require('f-validator')constequal=require('assert').deepStrictEqual// Every validator is just a functionconstvalidator1=stringequal(validator1('I am a string'),null)// passed check -> null// Some validator can use other validators// e.g. `or`, `optional`, `objectOf`, `arrayOf`constvalidator2=or(string,number)// To validate object, `objectOf` takes a schema where each field is a validatorconstvalidator3=objectOf({a: or(string,number),b: objectOf({c: optional(string)})})// To validate array, `arrayOf` takes a validator which will be used to check every elementconstvalidator4=arrayOf(validator3)constgood={a: 5,b: {c: 'I am also a string'}}constbad={a: 5,b: {c: 42}}equal(validator4([good,good]),null)equal(validator4([good,bad]),{// an object describing the diffpath: [1,'b','c'],// key-path pointing to the exact field to blameexpected: 'or(null or undefined, string)',received: 42,message: 'Path:\'1.b.c\', Expected: or(null or undefined, string), Received: \'42\''})// Sometimes, you'll need your own validator// any function can be used as a 'Validator' if it has this signature:/** * @param any subject, subject to check * @param []string path, a key-path pointing to the field * @returns * null, if it passes the check * Object error, an error object created with `error` utility */// Example 1: a humble even number validatorconstevenNumber=(subject,path=[])=>{if(typeofsubject=='number'&&(subject%2===0)){returnnull}else{returnerror(path,'an even number',subject)// keypath, expected, received}}// now it can be used by other validatorconstarrayOfEvenNumber=arrayOf(evenNumber)equal(arrayOfEvenNumber([2,4,6,9]),{path: [3],// the 4th elementexpected: 'an even number',received: 9,message: 'Path:\'3\', Expected: an even number, Received: \'9\''})// Example 2: a stringified-json-object-conforming-to-a-given-validator validatorconstjsonString=validator=>(subject,path=[])=>{letparsedtry{parsed=JSON.parse(subject)}catch(e){returnerror(path,`json string of (${validator.name})`,subject)}returnvalidator(parsed,path)// note: `path` should be passed to it}

API

1. Error constructor:

error(path:[]string, expected:string, received:any, message:?string ) - create an error object describing the diff, use it when creating your own validator

2. Basic type validators (most are tested using Object.prototype.toString.call(value))

object

array

string

number

boolean

date

regexp

Null - note the initial

Undefined - note the initial

empty - valid if value is null or undefined

regex(re:regexp) - valid if value matches regex re

3. Composite type validators:

objectOf(schema:object) - valid if value is an object where for every key of schema, value[key] is validated by schema[key]

arrayOf(v:Validator) - valid if value is an array where every element is validated by v

jsonString(v:Validator) - valid if value is an stringified object that is validated by v

4. Logical validators:

not(v:validator) - valid if value is invalidated by v

any - always valid

and(...vs:[]validator) - valid if value is validated by every validator of vs

or(...vs:[]validator) - valid if value is validated by every validator of vs

optional(v:validator) - valid if value is either validated by v or null/undefined

is(ref:any) - valid if value is strictly deeply equal to ref

oneOf(...refs:[]any) - valid if value is strictly deeply equal to any element of refs

5. Advanced validator:

like(ref:any) - valid if value has the same type/structure as ref (recursively)

Example:

constreference={a: 42,b: 'I am string',c: {d: ['apple']},e: optional(string)}constvalue={a: 0,b: 'I am another string',c: {d: ['pear','microsoft']},e: 'yep',// functions in ref are taken as validatorsextra: 'I am an extra field, I will be fine'}like(reference)(value)// null (is valid)