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

class-validator

Allows use of decorator and non-decorator based validation. Internally uses validator.js to perform validation. Class-validator works on both browser and node.js platforms.

Installation

npm install class-validator --save

Note: Please use at least npm@6 when using class-validator. From npm@6 the dependency tree is flattened, which is required by class-validator to function properly.

Usage

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

import {
  validate,
  validateOrReject,
  Contains,
  IsInt,
  Length,
  IsEmail,
  IsFQDN,
  IsDate,
  Min,
  Max,
} from 'class-validator';

export class Post {
  @Length(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

validate(post).then(errors => {
  // errors is an array of validation errors
  if (errors.length > 0) {
    console.log('validation failed. errors: ', errors);
  } else {
    console.log('validation succeed');
  }
});

validateOrReject(post).catch(errors => {
  console.log('Promise rejected (validation failed). Errors: ', errors);
});
// or
async function validateOrRejectExample(input) {
  try {
    await validateOrReject(input);
  } catch (errors) {
    console.log('Caught promise rejection (validation failed). Errors: ', errors);
  }
}

Passing options

The validate function optionally expects a ValidatorOptions object as a second parameter:

export interface ValidatorOptions {
  skipMissingProperties?: boolean;
  whitelist?: boolean;
  forbidNonWhitelisted?: boolean;
  groups?: string[];
  dismissDefaultMessages?: boolean;
  validationError?: {
    target?: boolean;
    value?: boolean;
  };

  forbidUnknownValues?: boolean;
  stopAtFirstError?: boolean;
}

It's highly advised to set forbidUnknownValues: true as it will prevent unknown objects from passing validation.

Validation errors

The validate method returns an array of ValidationError objects. Each ValidationError is:

{
    target: Object; // Object that was validated.
    property: string; // Object's property that haven't pass validation.
    value: any; // Value that haven't pass a validation.
    constraints?: { // Constraints that failed validation with error messages.
        [type: string]: string;
    };
    children?: ValidationError[]; // Contains all nested validation errors of the property
}

In our case, when we validated a Post object, we have such an array of ValidationError objects:

[{
    target: /* post object */,
    property: "title",
    value: "Hello",
    constraints: {
        length: "$property must be longer than or equal to 10 characters"
    }
}, {
    target: /* post object */,
    property: "text",
    value: "this is a great post about hell world",
    constraints: {
        contains: "text must contain a hello string"
    }
},
// and other errors
]

If you don't want a target to be exposed in validation errors, there is a special option when you use validator:

validator.validate(post, { validationError: { target: false } });

This is especially useful when you send errors back over http, and you most probably don't want to expose the whole target object.

Validation messages

You can specify validation message in the decorator options and that message will be returned in the ValidationError returned by the validate method (in the case that validation for this field fails).

import { MinLength, MaxLength } from 'class-validator';

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

There are few special tokens you can use in your messages:

$value - the value that is being validated
$property - name of the object's property being validated
$target - name of the object's class being validated
$constraint1, $constraint2, ... $constraintN - constraints defined by specific validation type

Example of usage:

import { MinLength, MaxLength } from 'class-validator';

export class Post {
  @MinLength(10, {
    // here, $constraint1 will be replaced with "10", and $value with actual supplied value
    message: 'Title is too short. Minimal length is $constraint1 characters, but actual is $value',
  })
  @MaxLength(50, {
    // here, $constraint1 will be replaced with "50", and $value with actual supplied value
    message: 'Title is too long. Maximal length is $constraint1 characters, but actual is $value',
  })
  title: string;
}

Also you can provide a function, that returns a message. This allows you to create more granular messages:

import { MinLength, MaxLength, ValidationArguments } from 'class-validator';

export class Post {
  @MinLength(10, {
    message: (args: ValidationArguments) => {
      if (args.value.length === 1) {
        return 'Too short, minimum length is 1 character';
      } else {
        return 'Too short, minimum length is ' + args.constraints[0] + ' characters';
      }
    },
  })
  title: string;
}

Message function accepts ValidationArguments which contains the following information:

value - the value that is being validated
constraints - array of constraints defined by specific validation type
targetName - name of the object's class being validated
object - object that is being validated
property - name of the object's property being validated

Validating arrays

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

import { MinLength, MaxLength } from 'class-validator';

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

This will validate each item in post.tags array.

Validating sets

If your field is a set and you want to perform validation of each item in the set you must specify a special each: true decorator option:

import { MinLength, MaxLength } from 'class-validator';

export class Post {
  @MaxLength(20, {
    each: true,
  })
  tags: Set<string>;
}

This will validate each item in post.tags set.

Validating maps

If your field is a map and you want to perform validation of each item in the map you must specify a special each: true decorator option:

import { MinLength, MaxLength } from 'class-validator';

export class Post {
  @MaxLength(20, {
    each: true,
  })
  tags: Map<string, string>;
}

This will validate each item in post.tags map.

Validating nested objects

If your object contains nested objects and you want the validator to perform their validation too, then you need to use the @ValidateNested() decorator:

import { ValidateNested } from 'class-validator';

export class Post {
  @ValidateNested()
  user: User;
}

Please note that nested object must be an instance of a class, otherwise @ValidateNested won't know what class is target of validation. Check also Validating plain objects.

It also works with multi-dimensional array, like :

import { ValidateNested } from 'class-validator';

export class Plan2D {
  @ValidateNested()
  matrix: Point[][];
}

Validating promises

If your object contains property with Promise-returned value that should be validated, then you need to use the @ValidatePromise() decorator:

import { ValidatePromise, Min } from 'class-validator';

export class Post {
  @Min(0)
  @ValidatePromise()
  userId: Promise<number>;
}

It also works great with @ValidateNested decorator:

import { ValidateNested, ValidatePromise } from 'class-validator';

export class Post {
  @ValidateNested()
  @ValidatePromise()
  user: Promise<User>;
}

Inheriting Validation decorators

When you define a subclass which extends from another one, the subclass will automatically inherit the parent's decorators. If a property is redefined in the descendant class decorators will be applied on it both from that and the base class.

import { validate } from 'class-validator';

class BaseContent {
  @IsEmail()
  email: string;

  @IsString()
  password: string;
}

class User extends BaseContent {
  @MinLength(10)
  @MaxLength(20)
  name: string;

  @Contains('hello')
  welcome: string;

  @MinLength(20)
  password: string;
}

let user = new User();

user.email = 'invalid email'; // inherited property
user.password = 'too short'; // password wil be validated not only against IsString, but against MinLength as well
user.name = 'not valid';
user.welcome = 'helo';

validate(user).then(errors => {
  // ...
}); // it will return errors for email, title and text properties

Conditional validation

The conditional validation decorator (@ValidateIf) can be used to ignore the validators on a property when the provided condition function returns false. The condition function takes the object being validated and must return a boolean.

import { ValidateIf, IsNotEmpty } from 'class-validator';

export class Post {
  otherProperty: string;

  @ValidateIf(o => o.otherProperty === 'value')
  @IsNotEmpty()
  example: string;
}

In the example above, the validation rules applied to example won't be run unless the object's otherProperty is "value".

Note that when the condition is false all validation decorators are ignored, including isDefined.

Whitelisting

Even if your object is an instance of a validation class it can contain additional properties that are not defined. If you do not want to have such properties on your object, pass special flag to validate method:

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

This will strip all properties that don't have any decorators. If no other decorator is suitable for your property, you can use @Allow decorator:

import {validate, Allow, Min} from "class-validator";

export class Post {

    @Allow()
    title: string;

    @Min(0)
    views: number;

    nonWhitelistedProperty: number;
}

let post = new Post();
post.title = 'Hello world!';
post.views = 420;

post.nonWhitelistedProperty = 69;
(post as any).anotherNonWhitelistedProperty = "something";

validate(post).then(errors => {
  // post.nonWhitelistedProperty is not defined
  // (post as any).anotherNonWhitelistedProperty is not defined
  ...
});

If you would rather to have an error thrown when any non-whitelisted properties are present, pass another flag to validate method:

import { validate } from 'class-validator';
// ...
validate(post, { whitelist: true, forbidNonWhitelisted: true });

Passing context to decorators

It's possible to pass a custom object to decorators which will be accessible on the ValidationError instance of the property if validation failed.

import { validate } from 'class-validator';

class MyClass {
  @MinLength(32, {
    message: 'EIC code must be at least 32 characters',
    context: {
      errorCode: 1003,
      developerNote: 'The validated string must contain 32 or more characters.',
    },
  })
  eicCode: string;
}

const model = new MyClass();

validate(model).then(errors => {
  //errors[0].contexts['minLength'].errorCode === 1003
});

Skipping missing properties

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

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

When skipping missing properties, sometimes you want not to skip all missing properties, some of them maybe required for you, even if skipMissingProperties is set to true. For such cases you should use @IsDefined() decorator. @IsDefined() is the only decorator that ignores skipMissingProperties option.

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, Min, Length } from 'class-validator';

export class User {
  @Min(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: undefined, // the default
}); // this will not pass validation since all properties get validated regardless of their groups

validate(user, {
  groups: [],
}); // this will not pass validation, (equivalent to 'groups: undefined', see above)

There is also a special flag always: true in validation options that you can use. This flag says that this validation must be applied always no matter which group is used.

Custom validation classes

If you have custom validation logic you can create a Constraint class:

First create a file, lets say CustomTextLength.ts, and define a new class:
```
import { ValidatorConstraint, ValidatorConstraintInterface, ValidationArguments } from 'class-validator';

@ValidatorConstraint({ name: 'customText', async: false })
export class CustomTextLength implements ValidatorConstraintInterface {
  validate(text: string, args: ValidationArguments) {
    return text.length > 1 && text.length < 10; // for async validations you must return a Promise<boolean> here
  }

  defaultMessage(args: ValidationArguments) {
    // here you can provide default error message if validation failed
    return 'Text ($value) is too short or too long!';
  }
}
```
We marked our class with @ValidatorConstraint decorator. You can also supply a validation constraint name - this name will be used as "error type" in ValidationError. If you will not supply a constraint name - it will be auto-generated.

Our class must implement ValidatorConstraintInterface interface and its validate method, which defines validation logic. If validation succeeds, method returns true, otherwise false. Custom validator can be asynchronous, if you want to perform validation after some asynchronous operations, simply return a promise with boolean inside in validate method.

Also we defined optional method defaultMessage which defines a default error message, in the case that the decorator's implementation doesn't set an error message.

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

import { Validate } from 'class-validator';
import { CustomTextLength } from './CustomTextLength';

export class Post {
  @Validate(CustomTextLength, {
    message: 'Title is too short or long!',
  })
  title: string;
}

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

And use validator as usual:

import { validate } from 'class-validator';

validate(post).then(errors => {
  // ...
});

You can also pass constraints to your validator, like this:

import { Validate } from 'class-validator';
import { CustomTextLength } from './CustomTextLength';

export class Post {
  @Validate(CustomTextLength, [3, 20], {
    message: 'Wrong post title',
  })
  title: string;
}

And use them from validationArguments object:

import { ValidationArguments, ValidatorConstraint, ValidatorConstraintInterface } from 'class-validator';

@ValidatorConstraint()
export class CustomTextLength implements ValidatorConstraintInterface {
  validate(text: string, validationArguments: ValidationArguments) {
    return text.length > validationArguments.constraints[0] && text.length < validationArguments.constraints[1];
  }
}

Custom validation decorators

You can also create a custom decorators. Its the most elegant way of using a custom validations. Lets create a decorator called @IsLongerThan:

Create a decorator itself:

import { registerDecorator, ValidationOptions, ValidationArguments } from 'class-validator';

export function IsLongerThan(property: string, validationOptions?: ValidationOptions) {
  return function (object: Object, propertyName: string) {
    registerDecorator({
      name: 'isLongerThan',
      target: object.constructor,
      propertyName: propertyName,
      constraints: [property],
      options: validationOptions,
      validator: {
        validate(value: any, args: ValidationArguments) {
          const [relatedPropertyName] = args.constraints;
          const relatedValue = (args.object as any)[relatedPropertyName];
          return typeof value === 'string' && typeof relatedValue === 'string' && value.length > relatedValue.length; // you can return a Promise<boolean> here as well, if you want to make async validation
        },
      },
    });
  };
}

Put it to use:

import { IsLongerThan } from './IsLongerThan';

export class Post {
  title: string;

  @IsLongerThan('title', {
    /* you can also use additional validation options, like "groups" in your custom validation decorators. "each" is not supported */
    message: 'Text must be longer than the title',
  })
  text: string;
}

In your custom decorators you can also use ValidationConstraint. Lets create another custom validation decorator called IsUserAlreadyExist:

Create a ValidationConstraint and decorator:

import {
  registerDecorator,
  ValidationOptions,
  ValidatorConstraint,
  ValidatorConstraintInterface,
  ValidationArguments,
} from 'class-validator';

@ValidatorConstraint({ async: true })
export class IsUserAlreadyExistConstraint implements ValidatorConstraintInterface {
  validate(userName: any, args: ValidationArguments) {
    return UserRepository.findOneByName(userName).then(user => {
      if (user) return false;
      return true;
    });
  }
}

export function IsUserAlreadyExist(validationOptions?: ValidationOptions) {
  return function (object: Object, propertyName: string) {
    registerDecorator({
      target: object.constructor,
      propertyName: propertyName,
      options: validationOptions,
      constraints: [],
      validator: IsUserAlreadyExistConstraint,
    });
  };
}

note that we marked our constraint that it will by async by adding { async: true } in validation options.

And put it to use:

import { IsUserAlreadyExist } from './IsUserAlreadyExist';

export class User {
  @IsUserAlreadyExist({
    message: 'User $value already exists. Choose another name.',
  })
  name: string;
}

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';
import { useContainer, Validator } from 'class-validator';

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

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

Synchronous validation

If you want to perform a simple non async validation you can use validateSync method instead of regular validate method. It has the same arguments as validate method. But note, this method ignores all async validations you have.

Manual validation

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

import { isEmpty, isBoolean } from 'class-validator';

isEmpty(value);
isBoolean(value);

Validation decorators

Decorator	Description
Common validation decorators
`@IsDefined(value: any)`	Checks if value is defined (!== undefined, !== null). This is the only decorator that ignores skipMissingProperties option.
`@IsOptional()`	Checks if given value is empty (=== null, === undefined) and if so, ignores all the validators on the property.
`@Equals(comparison: any)`	Checks if value equals ("===") comparison.
`@NotEquals(comparison: any)`	Checks if value not equal ("!==") comparison.
`@IsEmpty()`	Checks if given value is empty (=== '', === null, === undefined).
`@IsNotEmpty()`	Checks if given value is not empty (!== '', !== null, !== undefined).
`@IsIn(values: any[])`	Checks if value is in a array of allowed values.
`@IsNotIn(values: any[])`	Checks if value is not in a array of disallowed values.
Type validation decorators
`@IsBoolean()`	Checks if a value is a boolean.
`@IsDate()`	Checks if the value is a date.
`@IsString()`	Checks if the string is a string.
`@IsNumber(options: IsNumberOptions)`	Checks if the value is a number.
`@IsInt()`	Checks if the value is an integer number.
`@IsArray()`	Checks if the value is an array
`@IsEnum(entity: object)`	Checks if the value is an valid enum
Number validation decorators
`@IsDivisibleBy(num: number)`	Checks if the value is a number that's divisible by another.
`@IsPositive()`	Checks if the value is a positive number greater than zero.
`@IsNegative()`	Checks if the value is a negative number smaller than zero.
`@Min(min: number)`	Checks if the given number is greater than or equal to given number.
`@Max(max: number)`	Checks if the given number is less than or equal to given number.
Date validation decorators
`@MinDate(date: Date)`	Checks if the value is a date that's after the specified date.
`@MaxDate(date: Date)`	Checks if the value is a date that's before the specified date.
String-type validation decorators
`@IsBooleanString()`	Checks if a string is a boolean (e.g. is "true" or "false").
`@IsDateString()`	Alias for `@IsISO8601()`.
`@IsNumberString(options?: IsNumericOptions)`	Checks if a string is a number.
String validation decorators
`@Contains(seed: string)`	Checks if the string contains the seed.
`@NotContains(seed: string)`	Checks if the string not contains the seed.
`@IsAlpha()`	Checks if the string contains only letters (a-zA-Z).
`@IsAlphanumeric()`	Checks if the string contains only letters and numbers.
`@IsDecimal(options?: IsDecimalOptions)`	Checks if the string is a valid decimal value. Default IsDecimalOptions are `force_decimal=False`, `decimal_digits: '1,'`, `locale: 'en-US'`
`@IsAscii()`	Checks if the string contains ASCII chars only.
`@IsBase32()`	Checks if a string is base32 encoded.
`@IsBase64()`	Checks if a string is base64 encoded.
`@IsIBAN()`	Checks if a string is a IBAN (International Bank Account Number).
`@IsBIC()`	Checks if a string is a BIC (Bank Identification Code) or SWIFT code.
`@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.
`@IsEthereumAddress()`	Checks if the string is an Ethereum address using basic regex. Does not validate address checksums.
`@IsBtcAddress()`	Checks if the string is a valid BTC address.
`@IsDataURI()`	Checks if the string is a data uri format.
`@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).
`@IsFullWidth()`	Checks if the string contains any full-width chars.
`@IsHalfWidth()`	Checks if the string contains any half-width chars.
`@IsVariableWidth()`	Checks if the string contains a mixture of full and half-width chars.
`@IsHexColor()`	Checks if the string is a hexadecimal color.
`@IsHSLColor()`	Checks if the string is an HSL color based on CSS Colors Level 4 specification.
`@IsRgbColor(options?: IsRgbOptions)`	Checks if the string is a rgb or rgba color.
`@IsIdentityCard(locale?: string)`	Checks if the string is a valid identity card code.
`@IsPassportNumber(countryCode?: string)`	Checks if the string is a valid passport number relative to a specific country code.
`@IsPostalCode(locale?: string)`	Checks if the string is a postal code.
`@IsHexadecimal()`	Checks if the string is a hexadecimal number.
`@IsOctal()`	Checks if the string is a octal number.
`@IsMACAddress(options?: IsMACAddressOptions)`	Checks if the string is a MAC Address.
`@IsIP(version?: "4"\|"6")`	Checks if the string is an IP (version 4 or 6).
`@IsPort()`	Checks if the string is a valid port number.
`@IsISBN(version?: "10"\|"13")`	Checks if the string is an ISBN (version 10 or 13).
`@IsEAN()`	Checks if the string is an if the string is an EAN (European Article Number).
`@IsISIN()`	Checks if the string is an ISIN (stock/security identifier).
`@IsISO8601(options?: IsISO8601Options)`	Checks if the string is a valid ISO 8601 date format. Use the option strict = true for additional checks for a valid date.
`@IsJSON()`	Checks if the string is valid JSON.
`@IsJWT()`	Checks if the string is valid JWT.
`@IsObject()`	Checks if the object is valid Object (null, functions, arrays will return false).
`@IsNotEmptyObject()`	Checks if the object is not empty.
`@IsLowercase()`	Checks if the string is lowercase.
`@IsLatLong()`	Checks if the string is a valid latitude-longitude coordinate in the format lat, long.
`@IsLatitude()`	Checks if the string or number is a valid latitude coordinate.
`@IsLongitude()`	Checks if the string or number is a valid longitude coordinate.
`@IsMobilePhone(locale: string)`	Checks if the string is a mobile phone number.
`@IsISO31661Alpha2()`	Checks if the string is a valid ISO 3166-1 alpha-2 officially assigned country code.
`@IsISO31661Alpha3()`	Checks if the string is a valid ISO 3166-1 alpha-3 officially assigned country code.
`@IsLocale()`	Checks if the string is a locale.
`@IsPhoneNumber(region: string)`	Checks if the string is a valid phone numberusing libphonenumber-js.
`@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.
`@IsNumberString(options?: IsNumericOptions)`	Checks if the string is numeric.
`@IsSurrogatePair()`	Checks if the string contains any surrogate pairs chars.
`@IsUrl(options?: IsURLOptions)`	Checks if the string is an url.
`@IsMagnetURI()`	Checks if the string is a magnet uri format.
`@IsUUID(version?: "3"\|"4"\|"5"\|"all")`	Checks if the string is a UUID (version 3, 4, 5 or all ).
`@IsFirebasePushId()`	Checks if the string is a Firebase Push ID
`@IsUppercase()`	Checks if the string is uppercase.
`@Length(min: number, max?: number)`	Checks if the string's length falls in a range.
`@MinLength(min: number)`	Checks if the string's length is not less than given number.
`@MaxLength(max: number)`	Checks if the string's length is not more than given number.
`@Matches(pattern: RegExp, modifiers?: string)`	Checks if string matches the pattern. Either matches('foo', /foo/i) or matches('foo', 'foo', 'i').
`@IsMilitaryTime()`	Checks if the string is a valid representation of military time in the format HH:MM.
`@IsHash(algorithm: string)`	Checks if the string is a hash The following types are supported:`md4`, `md5`, `sha1`, `sha256`, `sha384`, `sha512`, `ripemd128`, `ripemd160`, `tiger128`, `tiger160`, `tiger192`, `crc32`, `crc32b`.
`@IsMimeType()`	Checks if the string matches to a valid MIME type format
`@IsSemVer()`	Checks if the string is a Semantic Versioning Specification (SemVer).
`@IsISSN(options?: IsISSNOptions)`	Checks if the string is a ISSN.
`@IsISRC()`	Checks if the string is a ISRC.
`@IsRFC3339()`	Checks if the string is a valid RFC 3339 date.
Array validation decorators
`@ArrayContains(values: any[])`	Checks if array contains all values from the given array of values.
`@ArrayNotContains(values: any[])`	Checks if array does not contain any of the given values.
`@ArrayNotEmpty()`	Checks if given array is not empty.
`@ArrayMinSize(min: number)`	Checks if the array's length is greater than or equal to the specified number.
`@ArrayMaxSize(max: number)`	Checks if the array's length is less or equal to the specified number.
`@ArrayUnique(identifier?: (o) => any)`	Checks if all array's values are unique. Comparison for objects is reference-based. Optional function can be speciefied which return value will be used for the comparsion.
Object validation decorators
`@IsInstance(value: any)`	Checks if the property is an instance of the passed value.
Other decorators
`@Allow()`	Prevent stripping off the property when no other constraint is specified for it.

Defining validation schema without decorators

You can define your validation schemas without decorators:

you can define it in the separate object
you can define it in the .json file

This feature maybe useful in the cases if:

are using es5/es6 and don't have decorators available
you don't have a classes, and instead using interfaces
you don't want to use model at all
you want to have a validation schema separate of your model
you want beautiful json-schema based validation models
you simply hate decorators

Here is an example of using it:

Create a schema object:

import { ValidationSchema } from 'class-validator';
export let UserValidationSchema: ValidationSchema = {
  // using interface here is not required, its just for type-safety
  name: 'myUserSchema', // this is required, and must be unique
  properties: {
    firstName: [
      {
        type: 'minLength', // validation type. All validation types are listed in ValidationTypes class.
        constraints: [2],
      },
      {
        type: 'maxLength',
        constraints: [20],
      },
    ],
    lastName: [
      {
        type: 'minLength',
        constraints: [2],
      },
      {
        type: 'maxLength',
        constraints: [20],
      },
    ],
    email: [
      {
        type: 'isEmail',
      },
    ],
  },
};

Same schema can be provided in .json file, depend on your wish.

import { registerSchema } from 'class-validator';
import { UserValidationSchema } from './UserValidationSchema';
registerSchema(UserValidationSchema); // if schema is in .json file, then you can simply do registerSchema(require("path-to-schema.json"));

Better to put this code in a global place, maybe when you bootstrap your application, for example in app.ts.

Validate your object using validation schema:

import { validate } from 'class-validator';
const user = { firstName: 'Johny', secondName: 'Cage', email: 'johny@cage.com' };
validate('myUserSchema', user).then(errors => {
  if (errors.length > 0) {
    console.log('Validation failed: ', errors);
  } else {
    console.log('Validation succeed.');
  }
});

That's it. Here "myUserSchema" is the name of our validation schema. validate method will perform validation based on this schema

Validating plain objects

Due to nature of the decorators, the validated object has to be instantiated using new Class() syntax. If you have your class defined using class-validator decorators and you want to validate plain JS object (literal object or returned by JSON.parse), you need to transform it to the class instance via using class-transformer).

Samples

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

Extensions

There are several extensions that simplify class-validator integration with other modules:

Release notes

See information about breaking changes and release notes here.

0.13.1 (2021-01-14)

Added

optional mather function has been added to the ArrayUnique decorator

Fixed

a typo was fixed in the error message generated by the IsUUID decorator
calling ValidationError.toString() doesn't result in an error when forbidNonWhitelisted parameter was used
fixed typo in error message generated by IsIn decorator
the @types/validator package is correctly installed
inlineSources option is enabled in tsconfig preventing various sourcemap errors when consuming the package

Changed

various dev dependencies has been updated

FAQs

What is class-validator?

Is class-validator popular?

Is class-validator well maintained?

Package last updated on 14 Jan 2021

Did you know?

Socket for GitHub automatically highlights issues in each pull request and monitors the health of all your open source dependencies. Discover the contents of your packages and block harmful activity before you install or update your dependencies.

Install

class-validator

What is class-validator?

What are class-validator's main functionalities?

Other packages similar to class-validator

class-validator

Table of Contents

Installation

Usage

Passing options

Validation errors

Validation messages

Validating arrays

Validating sets

Validating maps

Validating nested objects

Validating promises

Inheriting Validation decorators

Conditional validation

Whitelisting

Passing context to decorators

Skipping missing properties

Validation groups

Custom validation classes

Custom validation decorators

Using service container

Synchronous validation

Manual validation

Validation decorators

Defining validation schema without decorators

Validating plain objects

Samples

Extensions

Release notes

0.13.1 (2021-01-14)

Added

Fixed

Changed

Related posts

class-validator

What is class-validator?

What are class-validator's main functionalities?

Other packages similar to class-validator

joi

yup

ajv

express-validator

class-validator

Table of Contents

Installation

Usage

Passing options

Validation errors

Validation messages

Validating arrays

Validating sets

Validating maps

Validating nested objects

Validating promises

Inheriting Validation decorators

Conditional validation

Whitelisting

Passing context to decorators

Skipping missing properties

Validation groups

Custom validation classes

Custom validation decorators

Using service container

Synchronous validation

Manual validation

Validation decorators

Defining validation schema without decorators

Validating plain objects

Samples

Extensions

Release notes

0.13.1 (2021-01-14)

Added

Fixed

Changed

Related posts

Developers Burned by Elasticsearch’s License Change Aren’t Going Back, Despite Its Return to Open Source

How Socket Protects Against Revival Hijacking Attacks on PyPI

Introducing Dashboard Analytics