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The introduction to Reactive Programming you've been missing

(by @andrestaltz)

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This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

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function mapValues(obj, fn) {
  return Object.keys(obj).reduce((result, key) => {
    result[key] = fn(obj[key], key);
    return result;
  }, {});
}

function pick(obj, fn) {
  return Object.keys(obj).reduce((result, key) => {
    if (fn(obj[key])) {

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#Comprehensive Introduction to @ngrx/store By: @BTroncone

Also check out my lesson @ngrx/store in 10 minutes on egghead.io!

Update: Non-middleware examples have been updated to ngrx/store v2. More coming soon!

Table of Contents

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Type Safe JSON Decoding in Elm

The power of a Static Typed language can seem magical at first. But the goal here is to take a tiny peak behind that curtain.

Elm's implementation of JSON parsing is type safe and how it achieves that can seem like a mystery. Even though I got the code to work, it took me a while to fully understand how it works.

I'm writing it down here for 2 reasons. To help others gain a greater understanding of Types and so I don't forget what I learned.

Word of Caution

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(ns reduxish.state-tools
  (:require-macros [cljs.core.async.macros :refer [go go-loop]])
  (:require [cljs.core.async.impl.protocols :refer [WritePort ReadPort]]
            [cljs.core.async :refer [<!]]))

(defn channel? [ch]
  (and (satisfies? WritePort ch) (satisfies? ReadPort ch)))

(defn dispatch! [reducer state value]
  (println value)

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I wanted to figure out the fastest way to load non-critical CSS so that the impact on initial page drawing is minimal.

TL;DR: Here's the solution I ended up with: https://github.com/filamentgroup/loadCSS/

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For async JavaScript file requests, we have the async attribute to make this easy, but CSS file requests have no similar standard mechanism (at least, none that will still apply the CSS after loading - here are some async CSS loading conditions that do apply when CSS is inapplicable to media: https://gist.github.com/igrigorik/2935269#file-notes-md ).

Seems there are a couple ways to load and apply a CSS file in a non-blocking manner:

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CSP, Generators, Transducers etc. Reading List

• Communicating Sequential Processes

• Taming the Asynchronous Beast with CSP Channels in JavaScript

• CSP is Responsive Design

• Comparative Literate Programming

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let cache = new Map();
let pending = new Map();

function fetchTextSync(url) {
  if (cache.has(url)) {
    return cache.get(url);
  }
  if (pending.has(url)) {
    throw pending.get(url);
  }

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#!/bin/bash
# This hook is run after this virtualenv is activated.
# Place this file at $VIRTUAL_ENV/bin

# I usually drop something like this into my virtualenv's postactivate for some 
# quick and handy shortcuts to common Django commands.
# This way dropping in to do some work on any arbitrary project is as easy as:
# 1. workon <project name>
# 2. djr

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How to think about Monads

Initially, Monads are the biggest, scariest thing about Functional Programming and especially Haskell. I've used monads for quite some time now, but I didn't have a very good model for what they really are. I read Philip Wadler's paper Monads for functional programming and I still didnt quite see the pattern.

It wasn't until I read the blog post You Could Have Invented Monads! (And Maybe You Already Have.) that I started to see things more clearly.

This is a distillation of those works and most likely an oversimplification in an attempt to make things easier to understand. Nuance can come later. What we need when first learning something is a simple, if inaccurate, model.

This document assumes a beginner's knowledge of pure functional programming and Haskell with some brief encounters of Monads, e.g. [Functors, Applicatives, And