class-validator

What is class-validator?

The class-validator package is a TypeScript and JavaScript library that allows for validation of classes and objects using decorators and non-decorator based validation. It is commonly used to ensure data integrity before persistence or processing and is particularly useful when working with class-based models.

What are class-validator's main functionalities?

Declarative Validation Decorators

Allows the use of decorators to declare validation rules directly in the class model. For example, ensuring a property is not empty, is an integer, or is a valid email address.

{"@IsNotEmpty()": "public name: string;", "@IsInt()": "public age: number;", "@IsEmail()": "public email: string;"}

Custom Validation Classes

Enables the creation of custom validation classes that implement the ValidatorConstraintInterface. This allows for complex and custom validation logic that can be reused across different class properties.

{"@ValidatorConstraint({ async: false })": "class IsLongerThanConstraint implements ValidatorConstraintInterface { validate(text: string, args: ValidationArguments) { return text.length > args.constraints[0]; } defaultMessage(args: ValidationArguments) { return 'Text is too short. Should be longer than ' + args.constraints[0] + ' characters'; } }", "@ValidatorConstraint()": "@IsLongerThan(10, { message: 'Text must be longer than 10 characters' }) public text: string;"}

Validation of Nested Objects

Supports validation of nested objects using the ValidateNested decorator, ensuring that the properties of the nested objects also adhere to their respective validation rules.

{"@ValidateNested()": "@Type(() => SubClass) public nested: SubClass;"}

Asynchronous Validation

Provides asynchronous validation functions like validateOrReject, which can handle async validators and return a promise that either resolves if the object is valid or rejects with the validation errors.

{"@IsEmail({}, { message: 'Invalid email' })": "public email: string;", "validateOrReject(someObject)": ".catch(errors => { console.log('Promise rejected (validation failed). Errors: ', errors); });"}

Manual Validation

Allows for manual validation of objects without using decorators by calling the validate function, which returns a promise containing any validation errors.

{"validate(someObject)": ".then(errors => { if (errors.length > 0) { console.log('Validation failed: ', errors); } else { console.log('Validation succeed'); } });"}

Other packages similar to class-validator

joi

Joi is a powerful schema description language and data validator for JavaScript. Unlike class-validator, Joi does not use decorators and is schema-based. It is often used for object schema validation and can be used on both client and server sides.

yup

Yup is a JavaScript schema builder for value parsing and validation. It defines a schema with a more fluent/chainable API and is less verbose than class-validator. It is often used in the context of form validation, especially with form libraries like Formik.

ajv

Ajv is a JSON schema validator. It validates data against JSON Schema (draft 6, draft 7, and draft 2019-09). It is known for its performance and is used for validating JSON data structures, unlike class-validator which is more focused on class and object validation.

express-validator

Express-validator is a set of express.js middlewares that wraps validator.js, a library that provides validator and sanitizer functions. It is specifically designed for Express applications and allows for middleware-based validation, which is different from the decorator-based approach of class-validator.

README

class-validator

Allows to use decorator and non-decorator based validation in your Typescript classes. Internally uses validator.js to perform validation.

Release Notes

0.3.0

• package has changed its name from validator.ts to class-validator.
• sanitation functionality has been removed from this library. Use class-sanitizer instead.

Installation

1. Install module:

   npm install class-validator --save

2. Use typings to install all required definition dependencies.

   typings install

3. ES6 features are used, so you may want to install es6-shim too:

   npm install es6-shim --save

   if you are building nodejs app, you may want to require("es6-shim"); in your app. or if you are building web app, you man want to add <script src="path-to-shim/es6-shim.js"> on your page.

Usage

Create your class and put some validation decorators on its properties you want to validate:

import {validate} from "class-validator/class-validator";
import {Contains, IsInt, IsLength, IsEmail, IsFQDN, IsDate} from "class-validator/decorators";

export class Post {

    @IsLength(10, 20)
    title: string;

    @Contains('hello')
    text: string;

    @IsInt({ min: 0, max: 10 })
    rating: number;

    @IsEmail()
    email: string;

    @IsFQDN()
    site: string;

    @IsDate()
    createDate: Date;

}

let post = new Post();
post.title = 'Hello'; // should not pass
post.text = 'this is a great post about hell world'; // should not pass
post.rating = 11; // should not pass
post.email = 'google.com'; // should not pass
post.site = 'googlecom'; // should not pass

let errors = validate(post); // returns you array of errors

There are some additional functions you may want to use:

validateAsync(post); // returns Promise<Post> if validation success, throws error if validation fail
validateOrThrow(post); // performs validation and throws ValidationError if validation fail
isValid(post); // simply checks if given object is valid. Returns true if it is, false otherwise

Validation messages

You can specify validation message to decorator options and this message will be returned in ValidationError object returned by validate method in the case if validation for this field fail.

import {MinLength, MaxLength} from "class-validator/decorators";

export class Post {

    @MinLength(10, {
        message: "Title is too short"
    })
    @MaxLength(50, {
        message: "Title is too long"
    })
    title: string;
}

Validating arrays

If your field is an array and you want to perform validation of each item in the array you need to specify a special decorator option:

import {MinLength, MaxLength} from "class-validator/decorators";

export class Post {

    @MaxLength(20, {
        each: true
    })
    tags: string[];
}

This will validate each item in post.tags array.

Validating nested objects

If your object contains nested objects and you want validator to perform validation of them too, then you need to use special decorator:

import {ValidateNested} from "class-validator/decorators";

export class Post {

    @ValidateNested()
    user: User;

}

Skipping missing properties

Sometimes you may want to skip validation of the properties that does not exist in the validating object. This is usually desirable when you want to update some parts of the document, and want to validate only updated parts, but skip everything else, e.g. skip missing properties. In such situations you need to pass a special flag to validate method:

import {validate} from "class-validator/class-validator";
// ...
validate(post, { skipMissingProperties: true });

Validation groups

In different situations you may want to use different validation schemas of the same object. In such cases you can use validation groups.

import {validate} from "class-validator/class-validator";
import {MinNumber, Length} from "class-validator/decorators";

export class User {

    @MinNumber(12, {
        groups: ['registration']
    })
    age: number;

    @Length(2, 20, {
        groups: ['registration', 'admin']
    })
    name: string;
}

let user = new User();
user.age = 10;
user.name = 'Alex';

validate(user, {
    groups: ['registration']
}); // this will not pass validation

validate(user, {
    groups: ['admin']
}); // this will pass validation

validate(user, {
    groups: ['registration', 'admin']
}); // this will not pass validation

validate(user, {
    groups: []
}); // this will pass validation

Custom validation classes

If you have custom validation logic you want to use as annotations you can do it this way:

1. First create a file, lets say CustomTextLength.ts, and create there a new class:

   import {ValidatorInterface} from "class-validator/ValidatorInterface";
   import {ValidatorConstraint} from "class-validator/decorators";
   
   @ValidatorConstraint()
   export class CustomTextLength implements ValidatorInterface {
   
       validate(text: string): boolean {
           return text.length > 1 && text.length < 10;
       }
   
   }
   

   Your class should implement ValidatorInterface interface and its validate method, which defines logic for data if its valid or not.

2. Then you can use your new validation constraint in your class:

   import {Validate} from "class-validator/decorators";
   import {CustomTextLength} from "./CustomTextLength";
   
   export class Post {
   
       @Validate(CustomTextLength, {
           message: "Wrong post title"
       })
       title: string;
   
   }
   

   Here we set our newly created CustomTextLength validation constraint for Post.title.

3. Now you can use validator as usual:

   import {validate} from "class-validator/class-validator";
   
   validate(post);
   

Using service container

Validator supports service container in the case if want to inject dependencies into your custom validator constraint classes. Here is example how to integrate it with typedi:

import {Container} from "typedi/Container";
import {Validator} from "class-validator/class-validator";

// do this somewhere in the global application level:
let validator = Container.get(Validator);
validator.container = Container;

// now everywhere you can inject Validator class which will go from the container
// also you can inject classes using constructor injection into your custom ValidatorConstraints

Manual validation

There are several method exist in the Validator that allows to perform non-decorator based validation:

import Validator from "class-validator/class-validator";

// Validation methods

Validator.contains(str, seed);
Validator.equals(str, comparison);
Validator.isAfter(date, afterDate);
Validator.isAlpha(str);
Validator.isAlphanumeric(str);
Validator.isAscii(str);
Validator.isBase64(str);
Validator.isBefore(date, beforeDate);
Validator.isBoolean(str);
Validator.isBooleanString(str);
Validator.isByteLength(str, min, max);
Validator.isCreditCard(str);
Validator.isCurrency(str, options);
Validator.isDate(str);
Validator.isDecimal(str);
Validator.isDivisibleBy(str, num);
Validator.isEmail(str, options);
Validator.isFQDN(str, options);
Validator.isFloat(str, options);
Validator.isFullWidth(str);
Validator.isHalfWidth(str);
Validator.isVariableWidth(str);
Validator.isHexColor(str);
Validator.isHexadecimal(str);
Validator.isIP(str, version);
Validator.isISBN(str, version);
Validator.isISIN(str);
Validator.isISO8601(str);
Validator.isIn(str, values);
Validator.isInt(str, options);
Validator.isJSON(str);
Validator.isLength(str, min, max);
Validator.isLowercase(str);
Validator.isMobilePhone(str, locale);
Validator.isMongoId(str);
Validator.isMultibyte(str);
Validator.isNumeric(str);
Validator.isSurrogatePair(str);
Validator.isURL(str, options);
Validator.isUUID(str, version);
Validator.isUppercase(str);
Validator.matches(str, pattern, modifiers);

Validation decorators

Decorator	Description
@Contains(seed: string)	Checks if the string contains the seed.
@Equals(comparison: string)	Checks if the string matches the comparison.
@IsAfter(date: Date)	Checks if the string is a date that's after the specified date.
@IsAlpha()	Checks if the string contains only letters (a-zA-Z).
@IsAlphanumeric()	Checks if the string contains only letters and numbers.
@IsAscii()	Checks if the string contains ASCII chars only.
@IsBase64()	Checks if a string is base64 encoded.
@IsBefore(date: Date)	Checks if the string is a date that's before the specified date.
@IsBoolean()	Checks if a value is a boolean.
@IsBooleanString()	Checks if a string is a boolean (e.g. is "true" or "false").
@IsByteLength(min: number, max?: number)	Checks if the string's length (in bytes) falls in a range.
@IsCreditCard()	Checks if the string is a credit card.
@IsCurrency(options?: IsCurrencyOptions)	Checks if the string is a valid currency amount.
@IsDate()	Checks if the string is a date.
@IsDecimal()	Checks if the string represents a decimal number, such as 0.1, .3, 1.1, 1.00003, 4.0, etc.
@IsDivisibleBy(number: number)	Checks if the string is a number that's divisible by another.
@IsEmail(options?: IsEmailOptions)	Checks if the string is an email.
@IsFQDN(options?: IsFQDNOptions)	Checks if the string is a fully qualified domain name (e.g. domain.com).
@IsFloat(options?: IsFloatOptions)	Checks if the string is a float.
@IsFullWidth()	Checks if the string contains any full-width chars.
@IsHalfWidth()	Checks if the string contains any half-width chars.
@IsHexColor()	Checks if the string is a hexadecimal color.
@IsHexadecimal()	Checks if the string is a hexadecimal number.
@IsIP(version?: number)	Checks if the string is an IP (version 4 or 6).
@IsISBN(version?: number)	Checks if the string is an ISBN (version 10 or 13).
@IsISIN()	Checks if the string is an ISIN (stock/security identifier).
@IsISO8601()	Checks if the string is a valid ISO 8601 date.
@IsIn(values: any[])	Checks if the string is in a array of allowed values.
@IsInt(options?: IsIntOptions)	Checks if the string is an integer.
@IsJSON()	Checks if the string is valid JSON.
@IsLength(min: number, max?: number)	Checks if the string's length falls in a range.
@IsLowercase()	Checks if the string is lowercase.
@IsMobilePhone(locale: string)	Checks if the string is a mobile phone number.
@IsMongoId()	Checks if the string is a valid hex-encoded representation of a MongoDB ObjectId.
@IsMultibyte()	Checks if the string contains one or more multibyte chars.
@IsNull()	Checks if the string is null.
@IsNumeric()	Checks if the string is numeric.
@IsSurrogatePair()	Checks if the string contains any surrogate pairs chars.
@IsUrl(options?: IsURLOptions)	Checks if the string is a fully qualified domain name (e.g. domain.com).
@IsUUID(version?: number)	Checks if the string is a UUID (version 3, 4 or 5).
@IsUppercase()	Checks if the string is uppercase.
@IsVariableWidth()	Checks if the string contains a mixture of full and half-width chars.
@Matches(pattern: RegExp, modifiers?: string)	Checks if string matches the pattern. Either matches('foo', /foo/i) or matches('foo', 'foo', 'i').
@MinLength(min: number)	Checks if the string's length is not less then given number.
@MaxLength(max: number)	Checks if the string's length is not more then given number.
@MinNumber(min: number)	Checks if the given number is not less then given number.
@MaxNumber(max: number)	Checks if the given number is not more then given number.
@NotEmpty()	Checks if given value is not empty.
@NotEmptyArray()	Checks if given array is not empty.
@MinSize(min: number)	Checks if array's length is as minimal this number.
@MaxSize(max: number)	Checks if array's length is as maximal this number.

Samples

Take a look on samples in ./sample for more examples of usages.

FAQ

• Which node version is supported?

  This module is tested on > node 4.0, so its highly recommended if you install the latest version of node. If you are using old versions of node, the major dependency (afaik) of this module is on ES6 Promises, which are supported by some of the old versions of node too. In the case if your node version does not support promises you can try to npm install es6-shim module and include it to make promises work in your version of node.

• Is this library production-ready?

  The library is under active development, and needs better testing and contributions from community. If you want to use it in production its highly recommended to fix library version that you use in your package.json file. Personally I use it in production.

Todos

• cover with tests
• more validation options
• add support for json-schema based validation
• use something better then validator.js and solve string-only validation issues