bsy-validation

Light validation utilities for TypeScript classes. With bsy-validation, class properties are decorated with validators, and then plain objects can be validated against a class's validation schema.

Note that version 2 is a complete rewrite, and is not backwards compatible.

Installation

With yarn:

yarn add bsy-validation@2.x.x

With npm:

npm install --save bsy-validation@2.x.x

Ensure that you have experimentalDecorators and emitDecoratorMetadata enabled in your tsconfig.json.

Usage

First, decorate a class's properties with the @Validate decorator, supplying one or more Validators as arguments. All of the Validator classes can be found in the validator directory.

For example, here is a decorated Person class.

import {
  Validate, IntValidator, StringValidator, MaxLengthValidator, EmailValidator,
  PhoneValidator, DateValidator, NumberValidator
} from 'bsy-validation';
 
export class Person {
  @Validate(new IntValidator())
  id: number;
 
  @Validate(
    new StringValidator(),
    new MaxLengthValidator(50))
  name: string;
 
  @Validate(new PhoneValidator())
  phone: string;
 
  @Validate(new EmailValidator())
  email: string;
 
  @Validate(new DateValidator())
  dob: Date;
 
  @Validate(new NumberValidator())
  weight: number;
}

An object can be checked against this class's validation schema using an ObjectValidator instance. This class's validate method takes two arguments: An object to validate, and a the constructor of a @Validate-decorated class. It returns a promise that is resolved if the object is valid, or rejected with one or more errors if the object is invalid.

Here's an example of a valid Person object.

import { ObjectValidator } from 'bsy-validation';
 
import { Person } from './person';
 
const validator = new ObjectValidator();
 
// Joe Dirt is valid.
const joeDirt = {
  id: 42,
  name: 'Joe Dirte',
  phone: '530-444-5555',
  email: '[e-mail]',
  dob: '1983-09-19T00:00:00.000Z',
  weight: 205
};
 
validator
  .validate(joeDirt, Person)
  .then(() => console.log('Joe Dirt is valid.'));

The above logs "Joe Dirt is valid." Here's an example of an invalid object.

import { ObjectValidator } from 'bsy-validation';
 
import { Person } from './person';
 
const validator = new ObjectValidator();
 
// Donald Trump is invalid.
const emperorTrump = {
  id: 74.7, // Not a valid int.
  name: 'Trust me people, my name is Mister Magnificient Trump', // Too long.
  weight: 239 // A lie, but valid.
};
validator
  .validate(emperorTrump, Person)
  .catch(err => console.error(JSON.stringify(err, null, 2)));

The above logs an error that describes why the object is invalid.

{
  "code": "VAL_ERROR_LIST",
  "name": "ValidationErrorList",
  "detail": "Validation errors occurred.",
  "errors": [
    {
      "code": "VALIDATION_ERROR",
      "name": "ValidationError",
      "detail": "\"name\" must be at most 50 characters long.",
      "field": "name"
    },
    {
      "code": "VALIDATION_ERROR",
      "name": "ValidationError",
      "detail": "\"id\" must be a valid integer.",
      "field": "id"
    }
  ]
}

Validator Call Order

For a given @Validate-decorated property, validators are applied in order. If one of the validators fails, then execution halts. For example, in the Person class defined above, Person.name has two validators: StringValidator and MaxLengthValidator. StringValidator is applied first, then MaxLengthValidator is called if StringValidator passes.

const aryaStark = {
  name: false // Not a string.  A girl has no name.
};
 
validator
  .validate(aryaStark, Person)
  .catch(err => console.error(JSON.stringify(err, null, 2)));

In the above example, aryaStark.name is not a string, so MaxLengthValidator is never executed. The above logs the following error.

{
  "code": "VAL_ERROR_LIST",
  "name": "ValidationErrorList",
  "detail": "Validation errors occurred.",
  "errors": [
    {
      "code": "VALIDATION_ERROR",
      "name": "ValidationError",
      "detail": "\"name\" must be a string.",
      "field": "name"
    }
  ]
}

Null and Undefined

The built-in validators consider null and undefined properties to be valid. So, for example, an empty object is considered to be a valid Person. To ensure that a property is present and/or non-null, use the DefinedValidator and NotNullValidator.

In the following class, the message property must be defined, cannot be null, and must be a string.

class Greeting {
  @Validate(
    new DefinedValidator(),
    new NotNullValidator(),
    new StringValidator())
  message: string;
}

When defining custom validators, null and undefined values should be considered valid.

Custom Validators

To create a custom validator, implement the Validator interface. You must define a validate method that returns a boolean or a promise, and a getErrorMessage method that's used when validation fails. Here's an example.

// File: ./odd-number-validator.ts
import { Validator, NumberValidator } from 'bsy-validation';
 
class OddNumberValidator implements Validator {
  /**
   * Check that val is a number and is odd.
   */
  validate(val: any): boolean {
    const numVal = new NumberValidator();
 
    return val === undefined || val === null ||
      numVal.validate(val) && Number(val) % 2 === 1;
  }
 
  /**
   * Describe the validation error.
   */
  getErrorMessage(propName: string): string {
    return `"${propName}" must be an odd number.`;
  }
}

Then, use the validator as follows.

import { Validate, ObjectValidator } from 'bsy-validation';
 
import { OddNumberValidator } from './odd-number-validator';
 
class Preferences {
  @Validate(new OddNumberValidator())
  favoriteNumber: number;
}
 
new ObjectValidator()
  .validate({favoriteNumber: 18}, Preferences)
  .catch(err => console.error(JSON.stringify(err, null, 2)));

When run, the above prints the following error.

{
  "code": "VAL_ERROR_LIST",
  "name": "ValidationErrorList",
  "detail": "Validation errors occurred.",
  "errors": [
    {
      "code": "VALIDATION_ERROR",
      "name": "ValidationError",
      "detail": "\"favoriteNumber\" must be an odd number.",
      "field": "favoriteNumber"
    }
  ]
}