Cereale

Cereale is a lightweight TypeScript library that provides Spring-like decorators for JSON mapping and validation. Built with ZERO external dependencies, it simplifies the process of converting between plain JSON and class instances with full validation support.

Features

• Spring-like Decorators: Familiar @JsonSerialize, @JsonDeserialize, @JsonType, and @JsonPolymorphic.
• Custom Serializers/Deserializers: Easily handle complex types like Dates, BigInts, or custom objects.
• Polymorphism Support: Native handling of polymorphic types via discriminators.
• Integrated Validation: Automatically validates objects during serialization and deserialization.
• Type Safety: Fully written in TypeScript for excellent developer experience.
• Zero Dependencies: Extremely lightweight and fast.

Installation

npm install cereale

Make sure to enable experimentalDecorators and emitDecoratorMetadata in your tsconfig.json:

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "target": "ES2025"
  }
}

Quick Start

1. Define your Models

Use decorators to define how your data should be transformed and validated.

import { 
  IsString, 
  IsInt, 
  Min, 
  IsDate, 
  ValidateNested,
  JsonSerialize, 
  JsonDeserialize, 
  JsonPolymorphic, 
  JsonSerializer, 
  JsonDeserializer 
} from 'cereale';

// Custom Date Serializer
class DateSerializer implements JsonSerializer<Date, string> {
  serialize(value: Date): string {
    return value.toISOString().split('T')[0];
  }
}

class DateDeserializer implements JsonDeserializer<string, Date> {
  deserialize(value: string): Date {
    return new Date(value);
  }
}

abstract class Media {
  @IsString()
  abstract type: string;

  @IsString()
  title: string;
}

class Book extends Media {
  type = 'book';
  
  @IsString()
  author: string;

  @JsonSerialize(DateSerializer)
  @JsonDeserialize(DateDeserializer)
  @IsDate()
  publishedAt: Date;
}

class Library {
  @IsString()
  name: string;

  @ValidateNested({ each: true })
  @JsonPolymorphic('type', [
    { value: Book, name: 'book' }
  ])
  items: Media[];
}

2. Map JSON with Validation

Use standalone utility functions to handle the conversion process directly.

import { fromJson, toJson, JsonValidationError } from 'cereale';

async function main() {
  const json = '{"name": "Central Library", "items": [{"type": "book", "title": "The Great Gatsby", "author": "F. Scott Fitzgerald", "publishedAt": "1925-04-10"}]}';

  try {
    // Deserialize JSON to Class Instance
    const library = await fromJson(Library, json);
    console.log(library.name); // "Central Library"
    console.log(library.items[0] instanceof Book); // true

    // Serialize Class Instance back to JSON
    const outputJson = await toJson(library);
    console.log(outputJson);
  } catch (error) {
    if (error instanceof JsonValidationError) {
      console.error("Validation failed:", error.errors);
    }
  }
}

3. Modern Web Frameworks (Request Integration)

Cereale is compatible with Fetch-based frameworks like Hono, Next.js, and Remix. Use the fromRequest async helper.

import { fromRequest, toPlain } from 'cereale';

// Hono Example
app.post('/books', async (c) => {
  const book = await fromRequest(Book, c.req.raw);
  return c.json(await toPlain(book));
});

API Reference

Decorators

• @JsonSerialize(serializer: ClassConstructor<JsonSerializer>): Specifies a custom serializer for a property.
• @JsonDeserialize(deserializer: ClassConstructor<JsonDeserializer>): Specifies a custom deserializer for a property.
• @JsonType(typeFunction: () => ClassConstructor<any>): Explicitly sets the type for nested transformations.
• @JsonPolymorphic(discriminator: string, subTypes: { value: ClassConstructor<any>, name: string }[]): Configures polymorphic transformation based on a discriminator field.

Validation Decorators

Most validation decorators accept an optional ValidationOptions object:

• each: boolean: Apply validation to each element of an array.
• message: string | ((args: ValidationArguments) => string): Custom error message.

Decorator	Description
@IsString()	Checks if value is a string.
@IsNumber()	Checks if value is a number (and not NaN).
@IsInt()	Checks if value is an integer.
@IsBoolean()	Checks if value is a boolean.
@IsObject()	Checks if value is an object (not null/array).
@IsDate()	Checks if value is a valid Date object.
@IsDefined()	Checks if value is not null or undefined.
@IsOptional()	Skips other validations if value is null/undefined.
@IsNotEmpty()	Checks if value is not null/undefined/empty string.
@Min(value)	Checks if number is >= value.
@Max(value)	Checks if number is <= value.
@Positive()	Checks if number is > 0.
@Negative()	Checks if number is < 0.
@MinLength(len)	Checks if string length is >= len.
@MaxLength(len)	Checks if string length is <= len.
@Email()	Checks if string is a valid email.
@IsUrl()	Checks if string is a valid URL.
@Matches(regex)	Checks if string matches a regular expression.
@IsArray()	Checks if value is an array.
@ArrayNotEmpty()	Checks if array is not empty.
@ArrayMinSize(n)	Checks if array has at least n elements.
@ArrayMaxSize(n)	Checks if array has at most n elements.
@IsIn(values)	Checks if value is in the allowed list.
@IsNotIn(vals)	Checks if value is NOT in the list.
@ValidateNested()	Recursively validates nested objects/arrays.

Utilities

• toJson(obj: any): Validates and serializes an instance to a JSON string (Returns Promise<string>).
• toPlain(obj: any): Validates and transforms an instance to a plain object (Returns Promise<any>).
• fromJson(clazz: ClassConstructor, json: string): Parses JSON and transforms it to a validated class instance (Returns Promise<T>).
• toInstance(clazz: ClassConstructor, plain: any): Transforms a plain object to a validated class instance (Returns Promise<T>).
• fromRequest(clazz: ClassConstructor, request: Request): Extracts JSON from a Fetch Request and transforms it to a validated instance (Returns Promise<T>).
• validate(obj: any): Performs full validation on an object/instance (Returns Promise<ValidationError[]>).

Framework Integrations

Cereale is designed to be compatible with all trending web frameworks.

Hono / Next.js / Cloudflare Workers

Use fromRequest for seamless integration with the Fetch Request API.

NestJS

You can use Cereale inside your controllers for explicit mapping and validation without needing reflect-metadata.

import { toInstance } from 'cereale';

@Post()
async create(@Body() body: any) {
  const user = await toInstance(User, body);
  return this.userService.create(user);
}

Express / Fastify

Easily integrate with traditional Node.js frameworks.

import { toInstance, toPlain } from 'cereale';

app.post('/user', async (req, res) => {
  try {
    const user = await toInstance(User, req.body);
    res.json(await toPlain(user));
  } catch (err) {
    res.status(400).json(err);
  }
});

Contributing

Please see CONTRIBUTING.md for details on how to contribute to this project.

License

Cereale is licensed under the MIT License.