Typescript Object Validator

A simple library for typescript projects to validating object shapes. You can use this package to declare the shape you'd like an object to align to. This is handy when you have a complex object (for example, an API response) and want to validate the object, AND have typescript recognize the shape.

Basic Usage

import { validateObjectShape } from 'typescript-object-validator'
 
const elephantValidation = validateObjectShape(
    'Elephant API response' // https://elephant-api.herokuapp.com/elephants/random
    randomElephantResponse,
    {
        _id: 'string',
        index: 'number',
        name: 'string',
        affiliation: 'string',
        species: 'string',
        sex: 'string',
        fictional: 'boolean',
        dob: 'string',
        dod: 'string',
        wikilink: 'string',
        image: 'string',
        note: 'string',
    }
)
 
if (elephantValidation.valid === true) {
 
    /*
        At this point, elephantValidation.result will have the type of:
        {
            _id: 'string',
            index: 'number',
            name: 'string',
            affiliation: 'string',
            species: 'string',
            sex: 'string',
            fictional: 'boolean',
            dob: 'string',
            dod: 'string',
            wikilink: 'string',
            image: 'string',
            note: 'string',
        }
    */
 
    console.log(elephantValidation.result.name)
    // -> "Packy"
}
 

API

validateObjectShape Can be used to validate an object:

import { validateObjectShape } from 'typescript-object-validator'
 
validateObjectShape(
    objectDescription,
    validationItem,
    expectedObjectShape,
    validationOptions
)

• objectDescription (required - string): A description which is used in error messages when the object does not validate
• validationItem (required - object): An object you want to validate
• expectedObjectShape (required - object): A definition of what shape the object should match
• validationOptions (required - object): A set of options to change the validation behaviour, see more

The result of the validation is an object with a valid property which flags if the validation succeeded or failed, a result object which is the validated and typed object, or an errors array with error results.

const validationResult = validateObjectShape(
    objectDescription,
    validationItem,
    expectedObjectShape,
    validationOptions
)
 
// If the validation is successful
{
    valid: true,
    result: { ...validatedItem }  // (the object you passed in, but typed!)
}
 
// If the validation fails
{
    valid: false,
    errors: [
        'Expected Test obj.two to be type: number, was string',
    ]
}

validateObjectShape will coerce values for you if it's able to. For example if you say the property age is a number, but it's passed in as a string, validateObjectShape will try convert it to a number for you in the result object:

const validationResult = validateObjectShape(
    'Coercion Example',
    { age: '30' },
    { age: number }
)
 
if (validationResult.valid === true) {
    // validationResult.result.age -> 30
    typeof validationResult.result.age === 'number'
}

The library also alows you to test nested objects and arrays, for example:

const validationResult = validateObjectShape(
    'Nested Example',
    {
        age: '30',
        meta: { group: 'Staff' }
        names: [
            { fname: 'Jeff', lname: 'Thompson' },
            { fname: 'Jeff', lname: 'Thompson' }
        ]
    },
    {
        age: number,
        meta: { group: 'string' }
        names: arrayOf({ fname: 'string', lname: 'string' })
    }
)

Validation Types

There are a number of basic validation types available to use, and some helpers which allow you build more complex types:

Basic types

• string: Matches a string
• number: Matches a number
• boolean: Matches a boolean
• unknown: Matches an unknown type (will skip validation on that property)

This package also understands more complex types such as arrays and optional types. You can import helper functions to assist you in building these.

Complex Types:

• arrayOf ('string'): Array of some basic type
• optional ('string'): Makes the property your testing optional. The test will only run if the property exists

const result = validateObjectShape(
    'Test obj',
    {
        one: 'string value',
        two: 2,
        three: true,
        four: ['1', '2'],
        five: [true, false],
        six: [1, 2],
        seven: 'whatever'
    },
    {
        one: 'string',
        two: 'number',
        three: 'boolean',
        four: arrayOf('string'),
        five: arrayOf('boolean'),
        six: arrayOf('number'),
        seven: 'unknown',
        eight: optional('boolean')
    }
)

Options

• coerceValidObjectIntoArray (boolean): If you are validating an array with arrayOf, setting this to true will convert those properties to arrays for you, rather than returning an error. This is useful for example when converting from xml to json.

const validationResult = validateObjectShape(
    'Coercion Example',
    { names: { fname: 'Jeff', lname: 'Thompson' } },
    { names: arrayOf({ fname: 'string', lname: 'string' }) },
    { coerceValidObjectIntoArray: true }
)
 
/*
    Converts names into an array. validationResult.result:
    { names: [{ fname: 'Jeff', lname: 'Thompson' }] }
*/