oneRef.js

import EventEmitter from 'events';

export class Ref extends EventEmitter {

  constructor(v) {
    super();
    this._value = v;
  }

  getValue() {
    return this._value;
  } 

  /**
   * update contents of this ref cell and notify any listeners
   */
  setValue(v) {
    this._value = v;
    this.emit("change");
  }
}

/**
 * Given a Ref<A> returns an 'updater' function.
 *
 * An updater is a function that takes an ((A) => A) update function (uf),
 * applies it to the current value in ref and sets ref to the result (which
 * will notify registered listeners).
 *
 *     refUpdater: (ref: Ref<A>) => (uf: (A) => A) => void
 *
 * We use Currying here so that we can partially apply refUpdater
 * to obtain an updater function that can passed down to actions. 
 */
export const refUpdater = (ref) => (uf) => { ref.setValue(uf(ref.getValue())); };