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    0.9.1 • Public • Published


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    A simple plugin for class-transformer and class-validator which combines them in a nice and programmer-friendly API.


    Module installation

    npm install class-transformer-validator --save

    (or the short way):

    npm i -S class-transformer-validator

    Peer dependencies

    This package is only a simple plugin/wrapper, so you have to install the required modules too because it can't work without them. See detailed installation instruction for the modules installation:


    The usage of this module is very simple.

    import { IsEmail } from "class-validator";
    import { transformAndValidate } from "class-transformer-validator";
    // declare the class using class-validator decorators
    class User {
      public email: string;
      public hello(): string {
        return "World!";
    // then load the JSON string from any part of your app
    const userJson: string = loadJsonFromSomething();
    // transform the JSON to class instance and validate it correctness
    transformAndValidate(User, userJson)
      .then((userObject: User) => {
        // now you can access all your class prototype method
        console.log(`Hello ${userObject.hello()}`); // prints "Hello World!" on console
      .catch(err => {
        // here you can handle error on transformation (invalid JSON)
        // or validation error (e.g. invalid email property)

    You can also transform and validate plain JS object (e.g. from express req.body). Using ES7 async/await syntax:

    async (req, res) => {
      try {
        // transform and validate request body
        const userObject = await transformAndValidate(User, req.body);
        // infered type of userObject is User, you can access all class prototype properties and methods
      } catch (err) {
        // your error handling

    And since release 0.3.0 you can also pass array of objects - all of them will be validated using given class validation constraints:

    async (req, res) => {
      try {
        // transform and validate request body - array of User objects
        const userObjects = await transformAndValidate(User, req.body);
        userObjects.forEach(user => console.log(`Hello ${user.hello()}`));
      } catch (err) {
        // your error handling

    API reference

    Function signatures

    There is available the transformAndValidate function with three overloads:

    function transformAndValidate<T extends object>(
      classType: ClassType<T>,
      jsonString: string,
      options?: TransformValidationOptions,
    ): Promise<T | T[]>;
    function transformAndValidate<T extends object>(
      classType: ClassType<T>,
      object: object,
      options?: TransformValidationOptions,
    ): Promise<T>;
    function transformAndValidate<T extends object>(
      classType: ClassType<T>,
      array: object[],
      options?: TransformValidationOptions,
    ): Promise<T[]>;

    Be aware that if you validate json string, the return type is a Promise of T or T[] so you need to assert the returned type if you know the shape of json:

    const users = (await transformAndValidate(
      JSON.stringify([{ email: "test@test.test" }]),
    )) as User[];

    Or you can just check the type in runtime using Array.isArray method.

    Synchronous transformation and validation

    If you need sync validation, use transformAndValidateSync function instead (available since v0.4.0). It will synchronously return T or T[], not a Promise.

    Parameters and types

    • classType - an class symbol, a constructor function which can be called with new
    type ClassType<T> = {
      new (...args: any[]): T;
    • jsonString - a normal string containing JSON

    • object - plain JS object of type object (introduced in TypeScript 2.2), you will have compile-time error while trying to pass number, boolean, null or undefined but unfortunately run-time error when passing a function

    • array - array of plain JS objects like described above

    • options - optional options object, it has two optional properties

    interface TransformValidationOptions {
      validator?: ValidatorOptions;
      transformer?: ClassTransformOptions;

    You can use it to pass options for class-validator (more info) and for class-transformer (more info).

    More info

    The class-transformer and class-validator are more powerful than it was showed in the simple usage sample, so go to their github page and check out they capabilities!

    Release notes


    • widen class-transformer peer dependency version range to >=0.2.3
    • updated all dev dependencies


    • bump class-validator peer dependency to version >=0.12.0
    • updated TypeScript dependency to version ^3.9.5
    • updated all dev dependencies


    • updated class-transformer dependency to version ^0.2.3
    • updated class-validator dependency to version ^0.10.1
    • updated TypeScript dependency to version ^3.6.3
    • built code is now emitted as ES2015 (dropped es5 support)
    • updated all dev dependencies


    • updated class-transformer dependency to version ^0.2.0


    • updated class-validator dependency to version ^0.9.1


    • remove deprecated TransformValdiationOptions interface (typo)
    • updated class-validator dependency to version ^0.8.1 and class-transformer to ^0.1.9


    • fix TransformValdiationOptions interface name typo (deprecate in favour of TransformValidationOptions)


    • added transformAndValidateSync function for synchronous validation
    • changed return type for JSON's transform and validation to Promise of T or T[]
    • updated class-validator dependency to version ^0.7.2 and class-transformer to ^0.1.7


    • added support for transform and validate array of objects given class
    • updated class-validator dependency to version ^0.7.1


    • changed object parameter type declaration to object (introduced in TS 2.2)
    • throwing error when passed array, undefined or null



    • initial version with transformAndValidate function


    npm i class-transformer-validator

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    • michallytek