JSPM

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    AssemblyScript - v1.0.0-beta.18
  

📝 About

JSON is the de-facto serialization format of modern web applications, but its serialization and deserialization remain a significant performance bottleneck, especially at scale. Traditional parsing approaches are computationally expensive, adding unnecessary overhead to both clients and servers. This library is designed to mitigate this by leveraging SIMD acceleration and highly optimized transformations.

🚨 What's new in v1.0.0

🔹First release of v1.0.0

🔹Breaking changes to the way custom serializers/deserializers function (See Custom Serializers below)

🔹Major performance improvements and addition of SIMD

🔹Extremely low memory overhead compared to pre-1.x.x versions (great for serverless workloads)

🔹Fixes to many major issues and newly discovered bugs

🔹Full support for dynamic objects, arrays, and values

🔹Full support for JSON.Raw type everywhere

📚 Contents

• Installation
• Usage
• Examples
  • Omitting Fields
  • Nullable Primitives
  • Unknown or Dynamic Data
  • Using Raw JSON Strings
  • Custom Serializers
• Performance
• License
• Contact

💾 Installation

npm install json-as@1.0.0-beta.18

Add the --transform to your asc command (e.g. in package.json)

--transform json-as/transform --lib json-as/lib

Alternatively, add it to your asconfig.json

{
  "options": {
    "transform": ["json-as/transform"],
    "lib": ["json-as/lib"]
  }
}

If you'd like to see the code that the transform generates, run with JSON_DEBUG=true

🪄 Usage

import { JSON } from "json-as";


@json
class Vec3 {
  x: f32 = 0.0;
  y: f32 = 0.0;
  z: f32 = 0.0;
}


@json
class Player {

  @alias("first name")
  firstName!: string;
  lastName!: string;
  lastActive!: i32[];
  // Drop in a code block, function, or expression that evaluates to a boolean
  @omitif((self: Player) => self.age < 18)
  age!: i32;

  @omitnull()
  pos!: Vec3 | null;
  isVerified!: boolean;
}

const player: Player = {
  firstName: "Jairus",
  lastName: "Tanaka",
  lastActive: [2, 13, 2025],
  age: 18,
  pos: {
    x: 3.4,
    y: 1.2,
    z: 8.3,
  },
  isVerified: true,
};

const serialized = JSON.stringify<Player>(player);
const deserialized = JSON.parse<Player>(serialized);

console.log("Serialized    " + serialized);
console.log("Deserialized  " + JSON.stringify(deserialized));

🔍 Examples

🏷️ Omitting Fields

This library allows selective omission of fields during serialization using the following decorators:

@omit

This decorator excludes a field from serialization entirely.

@json
class Example {
  name!: string;

  @omit
  secret!: string;
}

const obj = new Example();
obj.name = "Visible";
obj.secret = "Hidden";

console.log(JSON.stringify(obj)); // { "name": "Visible" }

@omitnull

This decorator omits a field only if its value is null.

@json
class Example {
  name!: string;

  @omitnull()
  optionalField!: string | null;
}

const obj = new Example();
obj.name = "Present";
obj.optionalField = null;

console.log(JSON.stringify(obj)); // { "name": "Present" }

@omitif((self: this) => condition)

This decorator omits a field based on a custom predicate function.

@json
class Example {
  name!: string;

  @omitif((self: Example) => self.age < 18)
  age!: number;
}

const obj = new Example();
obj.name = "John";
obj.age = 16;

console.log(JSON.stringify(obj)); // { "name": "John" }

If age were 18 or higher, it would be included in the serialization.

🗳️ Using nullable primitives

AssemblyScript doesn't support using nullable primitive types, so instead, json-as offers the JSON.Box class to remedy it.

For example, this schema won't compile in AssemblyScript:

@json
class Person {
  name!: string;
  age: i32 | null = null;
}

Instead, use JSON.Box to allow nullable primitives:

@json
class Person {
  name: string;
  age: JSON.Box<i32> | null = null;
  constructor(name: string) {
    this.name = name;
  }
}

const person = new Person("Bob");
console.log(JSON.stringify(person)); // {"name":"Bob","age":null}

person.age = new JSON.Box<i32>(18); // Set age to 18
console.log(JSON.stringify(person)); // {"name":"Bob","age":18}

📤 Working with unknown or dynamic data

Sometimes it's necessary to work with unknown data or data with dynamic types.

Because AssemblyScript is a statically-typed language, that typically isn't allowed, so json-as provides the JSON.Value and JSON.Obj types.

Here's a few examples:

Working with multi-type arrays

When dealing with arrays that have multiple types within them, eg. ["string",true,null,["array"]], use JSON.Value[]

const a1 = JSON.parse<JSON.Value[]>('["string",true,null,["array"]]');
console.log(JSON.stringify(a[0])); // "string"
console.log(JSON.stringify(a[1])); // true
console.log(JSON.stringify(a[2])); // null
console.log(JSON.stringify(a[3])); // ["array"]

Working with unknown objects

When dealing with an object with an unknown structure, use the JSON.Obj type

const o1 = JSON.parse<JSON.Obj>('{"a":3.14,"b":true,"c":[1,2,3],"d":{"x":1,"y":2,"z":3}}');

console.log(o1.keys().join(" ")); // a b c d
console.log(
  o1
    .values()
    .map<string>((v) => JSON.stringify(v))
    .join(" "),
); // 3.14 true [1,2,3] {"x":1,"y":2,"z":3}

const y = o1.get("d").get<JSON.Obj>().get<i32>();
console.log('o1["d"]["y"] = ' + y.toString()); // o1["d"]["y"] = 2

Working with dynamic types within a schema

More often, objects will be completely statically typed except for one or two values.

In such cases, JSON.Value can be used to handle fields that may hold different types at runtime.

@json
class DynamicObj {
  id: i32 = 0;
  name: string = "";
  data!: JSON.Value; // Can hold any type of value
}

const obj = new DynamicObj();
obj.id = 1;
obj.name = "Example";
obj.data = JSON.parse<JSON.Value>('{"key":"value"}'); // Assigning an object

console.log(JSON.stringify(obj)); // {"id":1,"name":"Example","data":{"key":"value"}}

obj.data = JSON.Value.from<i32>(42); // Changing to an integer
console.log(JSON.stringify(obj)); // {"id":1,"name":"Example","data":42}

obj.data = JSON.Value.from("a string"); // Changing to a string
console.log(JSON.stringify(obj)); // {"id":1,"name":"Example","data":"a string"}

🏗️ Using Raw JSON strings

Sometimes its necessary to simply copy a string instead of serializing it.

For example, the following data would typically be serialized as:

const m1 = new Map<string, string>();
m1.set("pos", '{"x":1.0,"y":2.0,"z":3.0}');

const a1 = JSON.stringify(m1);
console.log("a1: " + a1);
// {"pos":"{\"x\":1.0,\"y\":2.0,\"z\":3.0}"}
// pos's value (Vec3) is contained within a string... ideally, it should be left alone

If, instead, one wanted to insert Raw JSON into an existing schema/data structure, they could make use of the JSON.Raw type to do so:

const m1 = new Map<string, JSON.Raw>();
m1.set("pos", new JSON.Raw('{"x":1.0,"y":2.0,"z":3.0}'));

const a1 = JSON.stringify(m1);
console.log("a1: " + a1);
// {"pos":{"x":1.0,"y":2.0,"z":3.0}}
// Now its properly formatted JSON where pos's value is of type Vec3 not string!

⚒️ Using custom serializers or deserializers

This library supports custom serialization and deserialization methods, which can be defined using the @serializer and @deserializer decorators.

Here's an example of creating a custom data type called Point which serializes to (x,y)

@json
class Point {
  x: f64 = 0.0;
  y: f64 = 0.0;
  constructor(x: f64, y: f64) {
    this.x = x;
    this.y = y;
  }


  @serializer
  serializer(self: Point): string {
    return `(${self.x},${self.y})`;
  }


  @deserializer
  deserializer(data: string): Point {
    const dataSize = bytes(data);
    if (dataSize <= 2) throw new Error("Could not deserialize provided data as type Point");

    const c = data.indexOf(",");
    const x = data.slice(1, c);
    const y = data.slice(c + 1, data.length - 1);

    return new Point(f64.parse(x), f64.parse(y));
  }
}

The serializer function converts a Point instance into a string format (x,y).

The deserializer function parses the string (x,y) back into a Point instance.

These functions are then wrapped before being consumed by the json-as library:

@inline __SERIALIZE_CUSTOM(ptr: usize): void {
  const data = this.serializer(changetype<Point>(ptr));
  const dataSize = data.length << 1;
  memory.copy(bs.offset, changetype<usize>(data), dataSize);
  bs.offset += dataSize;
}

@inline __DESERIALIZE_CUSTOM(data: string): Point {
  return this.deserializer(data);
}

This allows custom serialization while maintaining a generic interface for the library to access.

⚡ Performance

The json-as library has been optimized to achieve near-gigabyte-per-second JSON processing speeds through SIMD acceleration and highly efficient transformations. Below are some key performance benchmarks to give you an idea of how it performs.

Note: the AssemblyScript benches are run using a bump allocator so that Garbage Collection does not interfere with results. Also note that ideally, I would use d8, but until that is done, these results serve as a temporary performance comparison.

Table 1 - AssemblyScript

Table 2 - JavaScript

📃 License

This project is distributed under an open source license. You can view the full license using the following link: License

📫 Contact

Please send all issues to GitHub Issues and to converse, please send me an email at me@jairus.dev

• Email: Send me inquiries, questions, or requests at me@jairus.dev
• GitHub: Visit the official GitHub repository Here
• Website: Visit my official website at jairus.dev
• Discord: Contact me at My Discord or on the AssemblyScript Discord Server