memoize-observable.js

// http://stackoverflow.com/questions/7616461/generate-a-hash-from-string-in-javascript-jquery
const hashCode = (s) => {
  return s.split("").reduce(function(a,b){a=((a<<5)-a)+b.charCodeAt(0);return a&a},0);              
};

const memoizeObservable = (fn) => {
  let cache = {};
  
  return (...args) => {
    let entryKey = hashCode(JSON.stringify(args));
    
    if (cache[entryKey]) {
      return Rx.Observable.just(cache[entryKey]);
    }
    
    return fn.apply(null, args).map((value) => {
      cache[entryKey] = value;
      return value;
    }, (err) => {
      return err;
    });
  }
};

var memAjax = memoizeObservable(Rx.DOM.ajax);