Typescript Decorators

Air.js

class Air {

  @wetter
  humidity;

}

decorators.js

export function WaterDefault(target) {
	
  var original = target;
	
  function construct(constructor, args) {
    var c: any = function () {
      return constructor.apply(this, args);
    };
    c.prototype = constructor.prototype;
    return new c();
  }

  var f: any = function (...args) {
    return construct(original, args);
  };

  f.prototype = original.prototype;
	
  f.prototype.location = 'Prague';
  f.prototype.koeficient = '50';

  return f;
	
}

Earth.js

import twins from './twins';

export class Earth {

  trees: [string];

  constructor() {
    this.trees = [];
  }

  @twins
  public plant(seed) {
    this.trees.push(seed);
  }

}

twins.js

// Method decorator
// is represented by three mandatory arguments
// first argument target represent function which is going to be decorated
// second argument key represent name of decorated method
// third argument value represent property descriptor
export function twins(target: Function, key: string, value: any) {
  return {
    value: function(...args:[]) {
      var params = [];
      params.push(args[0]);
      params.push(args[0]);
      var result = value.value.apply(this, params);
      return result;
    }
  }
}

Water.js

import { WaterDefault } from './decorators';

@WaterDefault
export default class Water {
	
	hardness;
	purity;
	koeficient;
	
	constructor() {
		this.hardness = [ 'softer', 'soft', 'normal', 'hard', 'harder' ];
		this.purity = { 
			'london': 'clean',
			'prague': 'cleaner',
			'berlin': 'suck'
		}
	}
	
	public set location(value) {
		this._location = value.toLowerCase();
	}
	
	public get location() {
		return this._location;
	}
	
	public set koeficient(value) {
		this._koeficient = value;
	}
	
	public get koeficient() {
		return this._koeficient;
	}
	
	public quality() {
		return [
			this.purity[this.location],
			return(this.hardness[Math.round((this.koeficient / 100) * (this.hardness.length - 1))]);
		]
	}

}

wetter.js

// wetter decorator
// target is prototype of decorated class
// key is the name of decorated class
export default function wetter(target, key) {
  var _value = this[key];

  function getter() {
    return _value;
  }

  function setter(newValue) {
    if(newValue <= 90) newValue += 10;
    _value = newValue;
  }

  if(delete this[key]) {
    Object.defineProperty(target, key, {
        get: getter,
        set: setter
    });
  }
}