currying.js

const CELSIUS_SCALE = 'Celsius';
const FAHRENHEIT_SCALE = 'Fahrenheit';
const KELVIN_SCALE = 'Kelvin';


const TransformationMethodsHandler = function() {
  let collection = {};
  
  return {
    // Returns the transformation method by getting the source and target types
    get: function(source, target) {
      if(!collection[source] || !collection[source][target]) {
        return null;
      }
    
      return collection[source][target];
    },

    // Registers a new tranformation method using source and target as keys
    register: function(source, target, formula) {
      if(!collection[source]) {
        collection[source] = {};
      }
      if(!collection[source][target]) {
        collection[source][target] = {};
      }

      // Added transform property to make it more usable and readable from code
      collection[source][target].transform = formula;
    
      // Makes easier to keep on registering new methods
      return this;
    }
  };
}

let transformationHandler = new TransformationMethodsHandler()
  .register(CELSIUS_SCALE, KELVIN_SCALE, (degree) => degree + 273.15)
  .register(KELVIN_SCALE, CELSIUS_SCALE, (degree) => degree - 273.15)
  .register(CELSIUS_SCALE, FAHRENHEIT_SCALE, (degree) => (9*degree/5) + 32)
  .register(FAHRENHEIT_SCALE, CELSIUS_SCALE, (degree) => (5*(degree-32)) / 9)
  .register(FAHRENHEIT_SCALE, KELVIN_SCALE, (degree) => (5*(degree-32)) / 9 + parseFloat(273.15))
  .register(KELVIN_SCALE, FAHRENHEIT_SCALE, (degree) => (9*(degree - 273.15)/5) + 32);


let celsius = 24;
let fahrenheit = transformationHandler.get(CELSIUS_SCALE, FAHRENHEIT_SCALE).transform(celsius);
let kelvin = transformationHandler.get(FAHRENHEIT_SCALE, KELVIN_SCALE).transform(fahrenheit);
console.log(celsius, fahrenheit, kelvin); // 24, 75,.2, 297.15


// Singleton object to be used always in the same way
// Higher order functions to create the Parser object
// Currying technique to make code more readable
const Transformer = (function(engine) {
  return function(value) {
    return {
      from: function(source) {
        return {
          to: function(target) {
            return engine.get(source, target).transform(value);
          }
        };
      }
    };
  };
})(transformationHandler);


celsius = 24;
fahrenheit = Transformer(celsius).from(CELSIUS_SCALE).to(FAHRENHEIT_SCALE);
kelvin = Transformer(fahrenheit).from(FAHRENHEIT_SCALE).to(KELVIN_SCALE);
console.log(celsius, fahrenheit, kelvin); // 24, 75,.2, 297.15



let parserFromCelsius = Transformer(celsius).from(CELSIUS_SCALE);
fahrenheit = parserFromCelsius.to(FAHRENHEIT_SCALE);
kelvin = parserFromCelsius.to(KELVIN_SCALE);
console.log(celsius, fahrenheit, kelvin); // 24, 75,.2, 297.15