ts-parse

Parse JSON as typed instances.

Installation

npm install ts-parse

Prereqs

• TypeScript (for Decorator support)

• Enable emitDecoratorMetadata and experimentalDecorators in tsconfig.json:

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

Approach

Typed parsing utilizes constructor-based injection to create actual class instances from JSON or plain JavaScript objects. The Reflect Metadata shim, which is currently a ECMAScript proposal, exposes the type information of a constructor's parameters making it possible to instantiate objects from their real constructors.

For example:

@Constructable()
class Address {
 
  constructor(private city: string, private state: string, private zip: string) {
    
  }
  
  getCityStateZip(): string {
    return `${this.city}, ${this.state} ${this.zip}`;
  }
}
 
let address = TSON.parse('{"city":"Richmond","state":"VA","zip":"23230"}', Address);
 
address instanceof Address; // true
address.getCityStateZip(); // "Richmond, VA 23230"

The constructor in this example uses accessibility modifiers on the constructor args so that a corresponding instance member is also created, a nice feature of TypeScript.

Features

• Serialize JSON or POJOs to actual class instances
• Instantiation through construction injection
• Fully supports inheritance through super constructors
• Missing arguments in the constructor will be passed as NULL
• Extra JSON properties are set to the class instance via Object.assign

Array Support

Array support is built-in, but, it requires a cast for compile-time type support. This is necessary to support a simplified API and it eliminates the needs for an extra parsing method for Nth-degree Arrays (e.g. parseArray, parseArrayOfArrays, etc.).

@Constructable()
class Foo { }
 
const json = "[{},{}]";
 
// extra cast is required and can't be inferred
let foos = <Foo[]> TSON.parse(json, Foo);
foos[0] instanceof Foo; // true

@Constructable()
class Bar { }
 
const json = "[[{},{}]]";
 
// there's no limit to the amount of arrays that can be nested
let bars = <Bar[][]> TSON.parse(json, Bar);
bars[0][0] instanceof Bar; // true

Alternative Approach

Another approach is to creating instances would be member injection which this project does not support.

Tradeoffs and difficulties to field assignment:

• Annotate every member (the "code bloat" is a net zero tradeoff to the constructor "bloat")
• No support for inheritance - why? because we can't clearly define what properties to exclude getOwnProperties
• Assign to -> fields and setters
• How to handle -> readonly, private, protected, const

Contributing

• Fork and/or clone repo.
• Then npm install.
• Run a quick test npm run test.
• Make changes and run linter npm run lint.
• Submit a Pull Request!

For local testing, you may need to install globals:

• npm install mocha chai ts-node typings -g
• typings install dt~mocha --global --save
• typings install npm~chai --save