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d="M747.1,121.1V79.3c0-15.8-9.4-22.4-26.6-22.4c-15,0-26.8,6.6-26.8,19.3c0,2.4,0.2,3.3,0.8,5h16.6 c-0.5-2-0.7-5-0.7-7.5c0-9.6,3.6-12.4,9.4-12.4c6.4,0,9.7,2,9.7,14.4v11.2l-20.8,7.7c-10.6,4.1-19.3,8.8-19.3,20.7 c0,10.9,7.5,17.8,18.6,17.8c9.9,0,17.4-6.2,21.9-12.1v-0.1h0.1l0,11.1l26,0.1v-4.5C749.3,127.1,747.1,126.2,747.1,121.1z M729.6,117.8c-4.4,3.3-7.6,5.3-12.1,5.4c-7.7,0-11.2-5.2-11.2-12.6c0-7.7,3.6-11.2,9.8-13.5l13.4-5.4L729.6,117.8L729.6,117.8z"
></path>
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d="M0,0v90.4c0,65.7,50.9,88.5,88.1,105.2h0.1l3,1.4c0.7-0.4,1.4-0.7,2.2-1c0.4-0.2,0.9-0.4,1.3-0.6 c37.3-16.6,88.4-39.5,88.4-105V0H0z M116,132l-2-5.3l-26.6-70c-1.6,4.1-5.3,14-9.3,24.6l-15.3,41.3c-0.7,2-0.3,3,0.2,3.7 c1.1,1.3,3.5,1.3,7.3,1.3H71l0,4.4H42.4l0-4.4h2.2c3.9,0,7.1-1.7,9.5-6.5l2.9-6.6l26.5-67.8l-4.7-12.5h24.7l34.1,89.7l3.1,8.1H116z"
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<div class="bd-toc-item">
<h4 class="bd-toc-link">Web Applications II</h4>
</div>
<div class="bd-toc-item">
<a class="bd-toc-link" href="/web3/sprint/recq59MvEIZfUAohy">
1. Advanced React
</a>
<ul class="nav bd-sidenav">
<li>
<a href="/web3/module/recnDKrWb24lgaziC/">
Class Components
</a>
</li>
<li>
<a href="/web3/module/rec1DPoOZSmocXfak/">
The React Lifecycle
</a>
</li>
<li>
<a href="/web3/module/recAxmnYmusEi8JuL/">
Composing and Sharing Non-Visual Behavior
</a>
</li>
<li>
<a href="/web3/module/rechTQVfCg4p85Hoi/">
Testing Web Applications
</a>
</li>
</ul>
</div>
<div class="bd-toc-item">
<a class="bd-toc-link" href="/web3/sprint/recukritK1B1pFrcM">
2. Advanced State Management
</a>
<ul class="nav bd-sidenav">
<li>
<a href="/web3/module/rectpk6uIV3pCHJh8/">
The Reducer Pattern
</a>
</li>
<li class="active bd-sidenav-active">
<a href="/web3/module/recba2NUdVmgKYyR3/"> Redux </a>
</li>
<li>
<a href="/web3/module/recSoiWNJzGURrXYh/"> Async Redux </a>
</li>
<li>
<a href="/web3/module/recByjgF7FwwH5Z7W/"> Context API </a>
</li>
</ul>
</div>
<div class="bd-toc-item">
<a class="bd-toc-link" href="/web3/sprint/recnhsJGy28gNi1K5">
3. Advanced Web Applications
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<li>
<a href="/web3/module/recS9H6qCj0dQe32B/">
Testing React
</a>
</li>
<li>
<a href="/web3/module/recQlbCZf9tOVgiXC/">
Client-Side Authentication
</a>
</li>
<li>
<a href="/web3/module/recupVjaAKPqbuk7Y/">
HTTP / AJAX II
</a>
</li>
<li>
<a href="/web3/module/receOMvCB7dSyX5FL/">
Deploying Web Apps
</a>
</li>
</ul>
</div>
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<a class="bd-toc-link" href="/web3/sprint/recVFiuMBzbcZllxC">
4. WEB Unit 3 Build
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<div class="sticky-nav">
<div class="sprint-nav">
<ul class="section-nav">
<li class="toc-entry toc-h2"><a href="#prepare">Prepare</a></li>
<li class="toc-entry toc-h2"><a href="#learn">Learn</a></li>
<li class="toc-entry toc-h2">
<a href="#guided-project">Guided Project</a>
</li>
<li class="toc-entry toc-h2"><a href="#project">Project</a></li>
<li class="toc-entry toc-h2"><a href="#review">Review</a></li>
</ul>
</div>
</div>
<div class="wrapper limit-width">
<div class="flex-wrapper">
<div class="limit-width">
<div class="jumbotron">
<h1 class="bd-title" id="content">Redux</h1>
<span class="lead">
<p class="bd-lead"></p>
<p>
React is a very sophisticated UI - Component Library that
can be used together with a few other libraries to build
out large scale Single Page Applications. But as our
Application’s scale in size so too will the data that we
are concerned with within our applications. And you can
only start to imagine how difficult it might be manage all
of that data inside of React components. Redux is a
library that can help solve this problem by providing a
single source of truth for our data within our
application. As your team grows, and as your application
scales, Redux can help offset the pains that can be
brought on as a result of complexity.
</p>
</span>
<strong
>At the end of this module, you should be able to:</strong
>
<ul>
<li>explain what Redux is and the problem it solves</li>
<li>
create a Redux Store and connect it to a React application
</li>
<li>
use the connect() function to "connect" React components
to the Redux store
</li>
<li>
write Actions and Action Creators to describe state
changes
</li>
<li>
write Reducers to respond to actions and update state
</li>
</ul>
</div>
<div class="alert alert-warning" role="alert">
<h4>Pro Tip</h4>
<p>
Be on time. It’s a mark of respect not to keep others
waiting.
</p>
</div>
<h2 class="display-4">
<a
id="prepare"
class="anchor"
href="#prepare"
aria-hidden="true"
><span class="octicon octicon-link"></span></a
>Prepare
</h2>
<p class="lead">Review each preclass resource before class.</p>
<div class="preclass">
<ul class="list-group list-group-flush">
<li class="list-group-item">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/Ozx4FH4iKWc"
frameborder="0"
allowfullscreen
></iframe>
</div>
</li>
<li class="list-group-item">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/b0x1cwFX5rM"
frameborder="0"
allowfullscreen
></iframe>
</div>
</li>
<li class="list-group-item">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/gyJ31YLkYnU"
frameborder="0"
allowfullscreen
></iframe>
</div>
</li>
<li class="list-group-item">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/0rNVB36pQTE"
frameborder="0"
allowfullscreen
></iframe>
</div>
</li>
<li class="list-group-item">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/nF2HkjPz01A"
frameborder="0"
allowfullscreen
></iframe>
</div>
</li>
<li class="list-group-item">
<div class="embed-responsive embed-responsive-16by9">
<iframe
class="embed-responsive-item"
src="https://www.youtube.com/embed/VT9iMpTRexI"
frameborder="0"
allowfullscreen
></iframe>
</div>
</li>
<li class="list-group-item">
<a
target="_blank"
href="https://medium.com/@dan_abramov/smart-and-dumb-components-7ca2f9a7c7d0"
>Presentational and Container Components</a
>
<p>
A well thought out description of how we can think about
our components in react.
</p>
</li>
</ul>
</div>
<h2 class="display-4">
<a id="learn" class="anchor" href="#learn" aria-hidden="true"
><span class="octicon octicon-link"></span></a
>Learn
</h2>
<h4 class="mark mb-3 p-2">
Learn to explain what Redux is and the problem it solves
</h4>
<p>
Managing application state and keeping it in sync across all
layers of our application is very important.
</p>
<p>
Many bugs are caused by applications going into an
inconsistent state.
</p>
<h5>Overview</h5>
<p>
Redux is a predictable state management library for JavaScript
applications and is the most popular State container for React
applications. By now, we have discovered that building out
applications using React requires a lot of forethought to give
an application scalability. Specifically, we have noticed some
complications around the area of state-management. You may
have asked yourself a question like
<em
>“Which of my components should have state vs. which of my
components should just be a way to present some DOM
elements?”</em
>
</p>
<p>
Luckily you’re not alone in this dilemma. In fact, the
Facebook team that built React in the first place noticed that
managing state could become a nightmare at scale were they
only to use component state. So, they built a pattern, and
said, “everyone here at Facebook is going to write code after
this pattern.” This way, they could eliminate many of the
problems that unwieldy state-full components could surface.
That pattern was called
<code class="highlighter-rouge">Flux</code>
<a href="https://facebook.github.io/flux/docs/overview.html"
>link to docs</a
>, and it’s primary use case was to add some stringency to the
React ecosystem because by itself, React is very unopinionated
in how one should be designing their application and managing
state.
</p>
<p>
Flux was great, but developers had a hard time with
implementation because the pattern presented a few other
problems. Because of this, (and around the same time that
React was becoming so popular)
<a href="https://github.com/gaearon">Dan Abramov</a> built out
a ‘Time-traveling’ approach to debug an application. This
method eventually became known as Redux. Dan wanted to be able
to go back in time to see when/where the state had changed in
his application, and to do that, he ended up creating one of
the most popular state-management libraries known to React
Developers today.
</p>
<p>
Redux is a small, light-weight state container for use when
building JavaScript applications. Remember, Redux has nothing
to do with React other than the fact that many developers use
them together. The core concepts/principles of Redux are 3
fold:
</p>
<h4 id="the-store">The Store</h4>
<blockquote>
<p>
Everything that changes within your application is
represented by a single JavaScript Object known as the
store. The store contains our state for our application.
</p>
</blockquote>
<h4 id="application-state-is-immutable">
Application state is Immutable
</h4>
<blockquote>
<p>
When the application state changes, we clone the state
object, modify the clone, and replace the original state
with the new copy. We never mutate the original object, and
we never write to our store object.
</p>
</blockquote>
<h4 id="pure-functions-change-our-state">
Pure functions change our state
</h4>
<blockquote>
<p>
Given the same input, a pure function returns the same
output every time. All functions (reducers) in Redux must be
pure functions. Meaning they take in some state and a
description of what changes took place and return a copy of
our state.
</p>
</blockquote>
<p>
Redux is pretty simple at its core, the complications with
Redux arise when we try and implement it within a React
application. Usually, these issues are because there is some
new syntax, and it’s just a matter of time spent learning to
sort them out.
</p>
<h5>Follow Along</h5>
<p>
Watch the first 4 videos in
<a
href="https://egghead.io/lessons/react-redux-the-single-immutable-state-tree"
>this series</a
>
and try to wrap your head around how this would be useful in a
React application. Think of your projects that you’ve built in
React up until this point. What types of problems would Redux
have solved in those projects if any?
</p>
<h5>Challenge</h5>
<p>
Write your thoughts on why Redux exists and at least one
reason to use it as well as one reason to not use it.
</p>
<h5>Dig Deeper</h5>
<ul>
<li>
<a
href="https://www.smashingmagazine.com/2016/06/an-introduction-to-redux/"
target="blank_"
>Introduction to Redux</a
><br />
Article on Smashing Magazine that introduces the basics of
Redux
</li>
<li>
<a
href="https://code-cartoons.com/a-cartoon-intro-to-redux-3afb775501a6"
target="blank_"
>A Cartoon Intro to Redux</a
><br />
Article that explains the basics of Redux in an entertaining
manner
</li>
</ul>
<hr />
<h4 class="mark mb-3 p-2">
Learn to create a Redux Store and connect it to a React
application
</h4>
<p>
When using Redux, the state for the whole application is
contained inside the <em>Store</em>. This objective will guide
you through the process of what it takes to wire up a React
application to use Redux.
</p>
<h5>Overview</h5>
<p>
In this section, we’ll learn how to create the
<em>Redux Store</em> and how to use a library called
<code class="highlighter-rouge">react-redux</code> to connect
our React application to the <em>Store</em>. Because Redux is
a standalone library, (meaning it can be used on its own or
with another library/framework for state-management and data
flow) we have to use a second helper package that will enable
us to string together Redux within a React application. That
package is called
<a href="https://github.com/reduxjs/react-redux"
>React-Redux</a
>. Some more documentation and information lives
<a href="http://redux.js.org/basics/usage-with-react">here</a
>. The packages
<code class="highlighter-rouge">React</code> and
<code class="highlighter-rouge">Redux</code> are entirely
separate, as quoted in the Redux documentation.
</p>
<blockquote>
<p>
From the very beginning, we need to stress that Redux has no
relation to React. You can write Redux apps with React,
Angular, Ember, jQuery, or vanilla JavaScript.
</p>
</blockquote>
<h5>Follow Along</h5>
<p>
The first step we’re going to take to enable Redux within a
React application is to install it. This process assumes
you’ve used Create React App to boilerplate out a React
application.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="nx">npm</span> <span class="nx">install</span> <span class="nx">react</span><span class="o">-</span><span class="nx">redux</span> <span class="nx">redux</span>
</code></pre>
</div>
</div>
<p>
Now that we have
<code class="highlighter-rouge">redux</code> and
<code class="highlighter-rouge">react-redux</code> installed,
let’s learn how to set it up within our application. We will
use the
<code class="highlighter-rouge">createStore</code> function
from <code class="highlighter-rouge">redux</code>, so let’s
import that first.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="k">import</span> <span class="p">{</span> <span class="nx">createStore</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">'</span><span class="s1">redux</span><span class="dl">'</span><span class="p">;</span>
</code></pre>
</div>
</div>
<p>
<code class="highlighter-rouge">createStore</code> will take
in a single reducer that represents the state (data) of our
application globally. We need to create a
<code class="highlighter-rouge">store</code> variable, and use
<code class="highlighter-rouge">createStore</code> to create
the Redux store.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="kd">const</span> <span class="nx">store</span> <span class="o">=</span> <span class="nx">createStore</span><span class="p">(</span><span class="nx">reducer</span><span class="p">);</span>
</code></pre>
</div>
</div>
<p>
You’ll notice that we passed a reducer into
<code class="highlighter-rouge">createStore</code>, but we
don’t have a reducer yet. We’ll learn a lot more about
reducers soon. For now, let’s create a function called
<code class="highlighter-rouge">reducer</code> that returns an
object representing our state.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="kd">function</span> <span class="nx">reducer</span><span class="p">()</span> <span class="p">{</span>
<span class="k">return</span> <span class="p">{</span>
<span class="na">title</span><span class="p">:</span> <span class="dl">'</span><span class="s1">Hello world! I</span><span class="se">\'</span><span class="s1">m in the Redux store!</span><span class="dl">'</span><span class="p">,</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="kd">const</span> <span class="nx">store</span> <span class="o">=</span> <span class="nx">createStore</span><span class="p">(</span><span class="nx">reducer</span><span class="p">);</span>
</code></pre>
</div>
</div>
<p>
Now that we have a store, we want to make our application
aware of it. The way this works is that react-redux gives us a
<code class="highlighter-rouge"
><Provider></Provider></code
>
component that wraps around our entire application. We will
pass our newly created store to that component as a prop.
</p>
<p>
Within our Root Component (usually
<code class="highlighter-rouge">Index.js</code>), go ahead and
import <code class="highlighter-rouge">Provider</code> from
<code class="highlighter-rouge">react-redux</code>.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="k">import</span> <span class="p">{</span> <span class="nx">Provider</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">'</span><span class="s1">react-redux</span><span class="dl">'</span><span class="p">;</span>
</code></pre>
</div>
</div>
<p>
Then, all we need to do is wrap our
<code class="highlighter-rouge"><App/></code> with the
<code class="highlighter-rouge"><Provider></code>
component and pass a
<code class="highlighter-rouge">store</code> prop set equal to
the store we created. This will look like this:
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="o"><</span><span class="nx">Provider</span> <span class="nx">store</span><span class="o">=</span><span class="p">{</span><span class="nx">store</span><span class="p">}</span><span class="o">></span>
<span class="o"><</span><span class="nx">App</span><span class="o">/></span>
<span class="o"><</span><span class="sr">/Provider</span><span class="err">>
</span></code></pre>
</div>
</div>
<h5>Challenge</h5>
<p>
Let’s go ahead and take a peek at our application using the
React Dev Tools now that we’ve wrapped it up in a Provider
Component.
</p>
<p>
Now, take the time to think about where and when you’ve done
this before? Is there a package that we’ve used this same way?
If so, which package is it? It is important to note that a
large number of packages that we use in React are implemented
this way.
</p>
<p>
Write down a few thoughts on what you see, where you’ve seen
similar patterns, etc, and send that to your PM.
</p>
<hr />
<h4 class="mark mb-3 p-2">
Learn to use the connect() function to "connect" React
components to the Redux store
</h4>
<p>
Now that we have created a Redux store, we have to connect our
components to that store in order to access the data they will
need. We will use the connect function, and mapStateToProps to
accomplish this.
</p>
<h5>Overview</h5>
<p>
Now that we have built a store to manage our state, we need to
connect our components to that store. We can do so using the
<code class="highlighter-rouge">connect</code> function,
within the components themselves. We can also build a helper
function within the component files to tell the
<code class="highlighter-rouge">connect</code> function what
pieces of state we want to access. This function is usually
named <code class="highlighter-rouge">mapStateToProps</code>,
and it will map pieces of our Redux state to the props of our
component. Let’s try it out.
</p>
<h5>Follow Along</h5>
<p>
Using the app you created earlier that has the redux store
wired up, change the object you initially returned out of the
reducer function to look like this:
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre class="highlight"><code><span class="p">{</span>
<span class="nl">user</span><span class="p">:</span> <span class="p">{</span>
<span class="nl">name</span><span class="p">:</span> <span class="dl">'</span><span class="s1">Dustin</span><span class="dl">'</span>
<span class="p">},</span>
<span class="nx">movies</span><span class="p">:</span> <span class="p">[</span>
<span class="dl">'</span><span class="s1">Star Wars</span><span class="dl">'</span><span class="p">,</span>
<span class="dl">'</span><span class="s1">Lord of the Rings</span><span class="dl">'</span><span class="p">,</span>
<span class="dl">'</span><span class="s1">Harry Potter</span><span class="dl">'</span>
<span class="p">],</span>
<span class="nx">todoList</span><span class="p">:</span> <span class="p">[</span>
<span class="p">{</span> <span class="na">task</span><span class="p">:</span> <span class="dl">'</span><span class="s1">Learn Redux</span><span class="dl">'</span><span class="p">,</span> <span class="na">id</span><span class="p">:</span> <span class="mi">0</span><span class="p">,</span> <span class="na">completed</span><span class="p">:</span> <span class="kc">false</span> <span class="p">}</span>
<span class="p">],</span>
<span class="nx">moviesToWatch</span><span class="p">:</span> <span class="mi">13</span>
<span class="p">}</span>
</code></pre>
</div>
</div>
<p>
Now create a component called
<code class="highlighter-rouge">MovieList</code>. Next, we’ll
take a look at the syntax we use to connect our React
component to Redux, then we’ll talk about it. To start, import
the <code class="highlighter-rouge">connect</code> function
into your component:
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="k">import</span> <span class="p">{</span> <span class="nx">connect</span> <span class="p">}</span> <span class="k">from</span> <span class="dl">'</span><span class="s1">react-redux</span><span class="dl">'</span><span class="p">;</span>
</code></pre>
</div>
</div>
<p>
Next, we use the
<code class="highlighter-rouge">connect</code> function, where
we export the component at the bottom of the file. We invoke
<code class="highlighter-rouge">connect</code> twice (function
currying). First with two arguments - a function and an
object. Second with just the component we are trying to
connect. For now, we’ll pass
<code class="highlighter-rouge">null</code> and
<code class="highlighter-rouge">{}</code> into the first
invocation.
</p>
<div class="language-js highlighter-rouge">
<div class="highlight">
<pre
class="highlight"
><code><span class="c1">// export default MovieList; Not this way if we are connecting this component!</span>
<span class="k">export</span> <span class="k">default</span> <span class="nx">connect</span><span class="p">(</span><span class="kc">null</span><span class="p">,</span> <span class="p">{})(</span><span class="nx">MovieList</span><span class="p">)</span>
</code></pre>
</div>
</div>
<p>
Now <code class="highlighter-rouge">MovieList</code> is
connected to the store. Let’s write our
<code class="highlighter-rouge">mapStateToProps</code>
function now, to tell
<code class="highlighter-rouge">connect</code> which pieces of
our state we want to bring in to this component. This function
takes in <code class="highlighter-rouge">state</code> as a
parameter, then returns an object where the properties can be
passed to props, and the values are retrieved from the store
for our component.
</p>
<p>
For a
<code class="highlighter-rouge">MovieList</code> component, we
probably only want to know about the
<code class="highlighter-rouge">movies</code> array and the
<code class="highlighter-rouge">moviesToWatch</code> number,
<em>maybe</em> the
<code class="highlighter-rouge">user</code> object. We’ll not
worry about the
<code class="highlighter-rouge">todoList</code>, since our
component doesn’t need to know about that part of our state.
Let’s bring those three pieces of our state into the
component.
</p>