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0.5.36 • Public • Published


AssemblyScript WebAssembly

JSON for AssemblyScript focused on performance, low-overhead, and ease-of-use.


npm install json-as
npm install visitor-as --save-dev

For arbitrary-length numbers, use

npm install as-bignum

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

--transform json-as/transform

Alternatively, add it to your asconfig.json

  "options": {
    "transform": ["json-as/transform"]


import { JSON } from "json-as/assembly";

// @json or @serializable work here
class Vec3 {
  x!: f32;
  y!: f32;
  z!: f32;

class Player {
  firstName!: string;
  lastName!: string;
  lastActive!: i32[];
  age!: i32;
  pos!: Vec3 | null;
  isVerified!: boolean;

const player: Player = {
  firstName: "Emmet",
  lastName: "West",
  lastActive: [8, 27, 2022],
  age: 23,
  pos: {
    x: 3.4,
    y: 1.2,
    z: 8.3
  isVerified: true

const stringified = JSON.stringify<Player>(player);

const parsed = JSON.parse<Player>(stringified);

Planned Features

  • [x] Serialize
    • [x] Objects
    • [x] Other Types
    • [ ] Dynamic Types
  • [x] Deserialize
    • [x] Objects
    • [x] Other Types
    • [ ] Dynamic Types
  • [ ] Streaming API
  • [ ] Whitespace support
  • [ ] Integrate features from SIMDJson
  • [x] Optimize
    • [x] Strings
    • [x] Int/Float
    • [x] Bool
    • [x] Object Serialization
    • [ ] Object Parsing
    • [ ] Arrays


Number parsing speed has doubled over the last 5 versions due to the use of a atoi_fast function found in assembly/util.ts. This can be further optimized with SIMD.

String serialization has more than tripled in performance (+360%). The algorithm was rewritten for less if statements and more traps.

String deserialization was quadrupled from 3.4m ops to 14.8 ops (435%). It went from using .replaceAll to a specialized algorithm.

Schema (object) parsing is being optimized on GitHub and should be at least doubled if not tripled. (Current speed of barely-optimized version is 6.9m ops) This is due to taking advantage of the types with a type map and eliminating extra checking.

Serialize Object (Vec3): 6.7m ops/5s

Deserialize Object (Vec3): 3.8m ops/5s

Serialize Array (int[]): 6.6m ops/5s

Deserialize Array (int[]): 8.6m ops/5s

Serialize String (5): 5.9m ops/5s

Deserialize String (5): 16.3m ops/5s


Please submit an issue to https://github.com/JairusSW/as-json/issues if you find anything wrong with this library


npm i json-as

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  • jairussw