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---
layout: default
---
<header class="header">
<h1 class="title">JavaScript in <strong class="fourteen">14</strong> minutes</h1>
<p class="subtitle">by <a href="https://jgthms.com" target="_blank">Jeremy Thomas</a></p>
<div class="block">
<a href="https://bulma.io" target="_blank">
<img src="{{ site.url }}/images/made-with-bulma.png" alt="Made with Bulma" width="128" height="24">
</a>
</div>
<div class="content">
<p>Since you've already learned <a href="https://jgthms.com/web-design-in-4-minutes/" target="_blank">Web design in 4 minutes</a>, it's time to dive into the Web's main programming language: <strong>JavaScript</strong>.</p>
</div>
<!-- Case: noscript -->
<noscript>
<div class="message is-warning">
<div class="message-body">
To learn JavaScript, you need to enable it first!
<br>
<a href="https://www.enable-javascript.com/" target="_blank" rel="nofollow">Learn how to enable JavaScript in your web browser</a>.
</div>
</div>
<style type="text/css">#introduction{ display: none; }</style>
</noscript>
<!-- Case: mobile or tablet -->
<div class="case is-mobile is-tablet">
<div class="message is-warning">
<div class="message-body">
<p>
It looks like you're on a <strong><span class="case is-mobile">mobile device</span> <span class="case is-tablet">tablet</span></strong>! 😱
</p>
<p>
But fear not! 😊
</p>
<p>
While this tutorial is not optimized for this platform, I still made it readable enough for you to enjoy.
</p>
<p>
You should however revisit it on a desktop later if you can, to experience all the features!
</p>
<p>Anyway, <a onclick="showStep(1);">let's get started</a>!</p>
</div>
</div>
</div>
<!-- Case: desktop -->
<div id="introduction" class="case is-desktop">
<div class="content">
<p>I believe you are using this:</p>
<div id="platform" class="detect">
<div class="field">
<div class="label"><strong>Operating System</strong></div>
<div class="select">
<select id="os">
<option value="">---</option>
<option value="windows">Windows</option>
<option value="mac">Mac OS</option>
<option value="linux">Linux</option>
</select>
</div>
</div>
<div class="field">
<div class="label"><strong>Web Browser</strong></div>
<div class="select">
<select id="browser">
<option value="">---</option>
<option value="chrome">Google Chrome</option>
<option value="firefox">Mozilla Firefox</option>
<option value="safari">Apple Safari</option>
<option value="edge">Microsoft Edge</option>
<option value="opera">Opera</option>
</select>
</div>
</div>
</div>
<p>If this information is correct, let's <a onclick="showStep(1);">get started</a>.</p>
</div>
</div>
<!-- Case: return -->
<div id="return" class="message is-success">
<div class="message-body">
<p>
It looks that you've already been here! 😃
<br>
Do you want to <a id="resume">resume from where you left off</a> or <a id="reset">start over</a>?
</p>
</div>
</div>
</header>
<!-- 01 -->
<div id="step1" class="step">
<div class="content">
<h2>Console <span class="stamp is-tool">tool</span></h2>
<p>
Your browser comes with a <strong>developer console</strong> that allows you to type JavaScript directly in this webpage.
</p>
<div class="case is-chrome not-mobile not-tablet">
Since you're using <strong>Google Chrome</strong>, open the JavaScript console with
<span class="case is-windows is-linux"><kbd class="key">Ctrl</kbd><kbd class="plus">+</kbd><kbd class="key">Shift</kbd><kbd class="plus">+</kbd><kbd class="key">J</kbd> or <kbd class="key">F12</kbd></span>
<span class="case is-mac"><kbd class="key">option</kbd><kbd class="plus">+</kbd><kbd class="key">command</kbd><kbd class="plus">+</kbd><kbd class="key">J</kbd></span>
</div>
<div class="case is-firefox not-mobile not-tablet">
Since you're using <strong>Mozilla Firefox</strong>, open the Web console with
<span class="case is-windows is-linux"><kbd class="key">Ctrl</kbd><kbd class="plus">+</kbd><kbd class="key">Shift</kbd><kbd class="plus">+</kbd><kbd class="key">K</kbd> or <kbd class="key">F12</kbd></span>
<span class="case is-mac"><kbd class="key">option</kbd><kbd class="plus">+</kbd><kbd class="key">command</kbd><kbd class="plus">+</kbd><kbd class="key">K</kbd></span>
</div>
<div class="case is-edge not-mobile not-tablet">
Since you're using <strong>Microsoft Edge</strong>, open the JavaScript console with
<span class="case is-windows"><kbd class="key">F12</kbd></span>
</div>
<div class="case is-opera not-mobile not-tablet">
Since you're using <strong>Opera</strong>, open the JavaScript console with
<span class="case is-windows is-linux"><kbd class="key">Ctrl</kbd><kbd class="plus">+</kbd><kbd class="key">Shift</kbd><kbd class="plus">+</kbd><kbd class="key">I</kbd></span>
<span class="case is-mac"><kbd class="key">option</kbd><kbd class="plus">+</kbd><kbd class="key">command</kbd><kbd class="plus">+</kbd><kbd class="key">I</kbd></span>
</div>
<div class="case is-safari not-mobile not-tablet">
<p>Since you're using <strong>Apple Safari</strong>:</p>
<ol>
<li>Go to <strong>Preferences</strong> with <kbd class="key">command</kbd><kbd class="plus">+</kbd><kbd class="key">,</kbd></li>
<li>Go to the <strong>Advanced</strong> tab</li>
<li>Enable <strong>Show Develop menu in menu bar</strong></li>
<li>Open the JavaScript console <kbd class="key">option</kbd><kbd class="plus">+</kbd><kbd class="key">command</kbd><kbd class="plus">+</kbd><kbd class="key">C</kbd></li>
</ol>
</div>
<p>Let's see if it works!</p>
<p>In the console, type (or paste) the following, and press <kbd class="key">Enter</kbd></p>
</div>
{% capture snippet %}{% include snippets/snippet_hello_world.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
<!-- 02 -->
<div id="step2" class="step">
<div class="content">
{% include partials/gj.html %}
<p>You've just used <code>alert()</code>, a native <strong>JavaScript function</strong> that comes with every browser.</p>
<p>But what have you <a onclick="showStep(3);">done exactly</a>?</p></div>
</div>
</div>
<!-- 03 -->
<div id="step3" class="step">
<div class="content">
<h2>Functions <span class="stamp is-concept">concept</span></h2>
<p>You've <strong>called</strong> the <code>alert()</code> <em>function</em> with the <code>'Hello World!'</code> <em>argument</em>.</p>
<p>You have basically done 4 things:</p>
<div class="stabs">
<div class="stab">
<div class="stab-label">you typed the <strong>name</strong> of the function</div>
<div class="stab-code"><code class="stabilo"><span class="is-blue">alert</span>('Hello World!')</code></div>
</div>
<div class="stab">
<div class="stab-label">you opened a <strong>parenthesis</strong></div>
<div class="stab-code"><code class="stabilo">alert<span class="is-black">(</span>'Hello World!')</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed an <strong>argument</strong></div>
<div class="stab-code"><code class="stabilo">alert(<span class="is-green">'Hello World!'</span>)</code></div>
</div>
<div class="stab">
<div class="stab-label">you <strong>closed</strong> the parenthesis</div>
<div class="stab-code"><code class="stabilo">alert('Hello World!'<span class="is-black">)</span></code></div>
</div>
</div>
<p>Sometimes, there's no argument.<br>
Sometimes, there's multiple arguments.<br>
Most of them are required, but some of them can be optional.</p>
<p>In this case, <code>alert()</code> requires only one argument.</p>
<p>But what <a onclick="showStep(4);">type of argument</a> is that?</p>
</div>
</div>
<!-- 04 -->
<div id="step4" class="step">
<div class="content">
<h2>Strings <span class="stamp is-type">type</span></h2>
<p>When you handle text, you're using <strong>strings</strong>, which are a series of <em>characters</em>. In our case, we used a series of <strong>12 characters</strong>: <code>Hello World!</code>. This includes all lowercase and uppercase letters, the space, and the exclamation point.</p>
<p>To define where the string <em>starts</em> and where it <em>ends</em>, you need to wrap it in <strong>quotes</strong> (either single <code>'</code> or double <code>"</code>).</p>
<p>When you defined the <code>'Hello World!'</code> string:</p>
<ol>
<li>you typed a single <strong>quote</strong></li>
<li>you typed the <strong>12 characters</strong></li>
<li>you typed another single <strong>quote</strong></li>
</ol>
<p>What if you wanted to deal with <a onclick="showStep(5);">numbers instead</a>?</p>
</div>
</div>
<!-- 05 -->
<div id="step5" class="step">
<div class="content">
<h2>Numbers <span class="stamp is-type">type</span></h2>
<p>Like any other programming language, JavaScript can handle <strong>numbers</strong>.</p>
<p>These numbers can be big or small, with or without decimals, combined through numeric operations…</p>
<p>Type or paste the following snippet in your console:</p>
</div>
{% capture snippet %}{% include snippets/snippet_numbers.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
<!-- 06 -->
<div id="step6" class="step">
<div class="content">
{% include partials/gj.html title="Perfect!" %}
<p>Notice a few things:</p>
<ul>
<li>you're using the <code>+</code> and <code>*</code> <strong>operators</strong></li>
<li>the <strong>mathematical order</strong> is respected: first <code>5 * 3</code> is calculated, then <code>9 + 15</code></li>
<li>the <strong>spaces</strong> around the <code>*</code> symbol don't affect the output ; they're just here to help us (humans!) <em>read</em> the code.</li>
</ul>
<p>You can find numbers in <a onclick="showStep(7);">lots of places</a>.</p>
</div>
</div>
<!-- 07 -->
<div id="step7" class="step">
<div class="content">
<h2>Browser dimensions <span class="stamp is-info">info</span></h2>
<p>Numbers are everywhere! Especially in a browser.</p>
<p>For example, your current browser window has a certain <strong>width</strong> that you can access with JavaScript.</p>
<p>Type the following:</p>
{% capture snippet %}{% include snippets/snippet_innerwidth.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 08 -->
<div id="step8" class="step">
<div class="content">
{% include partials/gj.html title="Wonderful!" %}
<p>
This means your browser's window is <strong id="browserWidth">1680</strong> pixels wide.
</p>
<p>
As you would have guessed, <code>window.innerHeight</code> exists as well, as does <code>window.scrollY</code>, which gives you the current scroll position.
</p>
<p>But what is <code>window</code> <a onclick="showStep(9);">exactly</a>?</p>
</div>
</div>
<!-- 09 -->
<div id="step9" class="step">
<div class="content">
<h2>Objects <span class="stamp is-type">type</span></h2>
<p>
<code>window</code> is a JavaScript <strong>object</strong>.
</p>
<p>
<code>innerWidth</code> is a <strong>property</strong> of the <code>window</code> object.
<br>
To access this property, you used a dot <code>.</code> to specify you wanted the <code>innerWidth</code> that exists <em>within</em> the <code>window</code> object.
</p>
<p>The JavaScript object is basically a <strong>type</strong> that contains other things.</p>
<p>For example, <code>window</code> also has:</p>
<ul>
<li><code>window.origin</code> which is a string</li>
<li><code>window.scrollY</code> which is a number</li>
<li><code>window.location</code> which is an object</li>
</ul>
<p>If <code>window</code> is an object that contains <code>location</code> which is another object, this means that <a onclick="showStep(10);">JavaScript objects support</a>…</p>
</div>
</div>
<!-- 10 -->
<div id="step10" class="step">
<div class="content">
<h2>Nesting <span class="stamp is-info">info</span></h2>
<p>A property of an object can be an object itself (inception!).</p>
<p>Since <code>window.location</code> is an object too, it has properties of its own. To access these properties, just add another dot <code>.</code> and the name of the property.</p>
<p>For example, the <code>href</code> property exists:</p>
{% capture snippet %}{% include snippets/snippet_href.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 11 -->
<div id="step11" class="step">
<div class="content">
{% include partials/gj.html title="Awesome!" %}
<p>You just displayed the <strong>full URL</strong> of this webpage. This is because:</p>
<ul>
<li><code>window</code> is an object</li>
<li><code>location</code> is an object</li>
<li><code>href</code> is a string</li>
</ul>
<p>
There's no limit to how deeply objects can be nested.
<br>
There's also no limit to the number of properties an object can have.
</p>
<p>
As we've seen, the properties of an object can be of any type: strings, numbers, objects, and even functions. In the latter case, it's <a onclick="showStep(12);">called…</a>
</p>
</div>
</div>
<!-- 12 -->
<div id="step12" class="step">
<div class="content">
<h2>Methods <span class="stamp is-info">info</span></h2>
<p>When an object's <strong>property</strong> is a <strong>function</strong>, it's called a <strong>method</strong> instead.</p>
<p>Actually, the <code>alert()</code> function we've been using so far is a method of the <code>window</code> object!</p>
{% capture snippet %}{% include snippets/snippet_omg.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 13 -->
<div id="step13" class="step">
<div class="content">
{% include partials/gj.html title="OMG indeed!" %}
<p>
Since <code>window</code> is the top-level object in the browser, you can access all its properties and methods directly.
</p>
<p>
That's why typing <code>location.href</code> is the same as typing <code>window.location.href</code>.
</p>
<p>
Or why <code>alert()</code> is equivalent to <code>window.alert()</code>.
</p>
<p>
Objects are useful for grouping several properties under the same name and scope, and defining a <strong>hierarchy</strong> in the data. It's like a tree, where each branch can have other smaller branches.
</p>
<p>
But what if you only needed a <a onclick="showStep(14);">list of things</a>…
</p>
</div>
</div>
<!-- 14 -->
<div id="step14" class="step">
<div class="content">
<h2>Arrays <span class="stamp is-type">type</span></h2>
<p>A JavaScript <strong>array</strong> is a type that can contain multiple values, as if they were in an ordered list.</p>
<p>Let's pass an array of <strong>3 strings</strong> to the <code>alert()</code> function:</p>
{% capture snippet %}{% include snippets/snippet_what_is_up.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 15 -->
<div id="step15" class="step">
<div class="content">
{% include partials/gj.html title="Exactly!" %}
<p>
You already know the syntax for calling the <code>alert</code> function: <code>alert(argument)</code>.
</p>
<p>
In this case, the argument you passed is an array with 3 items that you have defined like this:
</p>
<div class="stabs">
<div class="stab">
<div class="stab-label">you opened a <strong>square bracket</strong></div>
<div class="stab-code"><code class="stabilo"><span class="is-black">[</span>'What', 'is', 'up']</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed the <strong>first item</strong> of the array, a string</div>
<div class="stab-code"><code class="stabilo">[<span class="is-green">'What'</span>, 'is', 'up']</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed a <strong>comma</strong> to separate the items</div>
<div class="stab-code"><code class="stabilo">['What'<span class="is-black">,</span> 'is', 'up']</code></div>
</div>
<div class="stab">
<div class="stab-label">you added <strong>two other items</strong> to the list</div>
<div class="stab-code"><code class="stabilo">['What', <span class="is-green">'is'</span><span class="is-black">, </span><span class="is-green">'up'</span>]</code></div>
</div>
<div class="stab">
<div class="stab-label">you <strong>closed</strong> the square bracket</div>
<div class="stab-code"><code class="stabilo">['What', 'is', 'up'<span class="is-black">]</span></code></div>
</div>
</div>
<p>
An array can contain any <strong>type</strong> of values: strings, numbers, objects, other arrays, and <em>more</em>…
</p>
<p>
Try out this snippet:
</p>
{% capture snippet %}{% include snippets/snippet_list.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 16 -->
<div id="step16" class="step">
<div class="content">
{% include partials/gj.html title="True!" %}
<p>
The first item <code>2 + 5</code> is a number, while the second one <code>'samurai'</code> is a string.
</p>
<p>
What about the <strong>third argument</strong>? It's not a string because it's not wrapped in quotes, and it's not a number either.
</p>
<p>
So <a onclick="showStep(17);">what is it</a>?
</p>
</div>
</div>
<!-- 17 -->
<div id="step17" class="step">
<div class="content">
<h2>Booleans <span class="stamp is-type">type</span></h2>
<p>While strings and numbers have an infinite amount of <em>possible</em> values, a <strong>boolean</strong> can only be either <code>true</code> or <code>false</code>.</p>
<p>
By combining the <code>alert()</code> function and the 3-item array on a <em>single</em> line, it makes our code less readable.
</p>
<p>
What if we could split the two by moving the array onto <a onclick="showStep(18);">its own line</a>?
</p>
</div>
</div>
<!-- 18 -->
<div id="step18" class="step">
<div class="content">
<h2>Variables <span class="stamp is-concept">concept</span></h2>
<p>
We can move the array into a <strong>variable</strong>.
</p>
<p>
A variable is a <strong>container</strong> that stores a certain <strong>value</strong>. It has a <strong>name</strong> (so you can identify and re-use it), and it has a <strong>value</strong> (so you can update it later on).
</p>
{% capture snippet %}{% include snippets/snippet_array.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet skipRun=true %}
<ul>
<li>
<code>my_things</code> is the <strong>name</strong> of the variable
</li>
<li>
<code>[2 + 5, 'samurai', true]</code> is the <strong>value</strong> of the variable
</li>
</ul>
<p>
Here's the breakdown:
</p>
<div class="stabs is-vertical">
<div class="stab">
<div class="stab-label">you typed the <strong>keyword</strong> <code>var</code></div>
<div class="stab-code"><code class="stabilo"><span class="is-purple">var</span> my_things = [2 + 5, 'samurai', true];</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed the <strong>name</strong> of the variable</div>
<div class="stab-code"><code class="stabilo">var <span class="is-blue">my_things</span> = [2 + 5, 'samurai', true];</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed the <strong>assignment</strong> operator <code>=</code></div>
<div class="stab-code"><code class="stabilo">var my_things <span class="is-purple">=</span> [2 + 5, 'samurai', true];</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed the <strong>array</strong></div>
<div class="stab-code"><code class="stabilo">var my_things = <span class="is-black">[</span><span class="is-red">2</span><span class="is-purple"> + </span><span class="is-red">5</span><span class="is-black">, </span><span class="is-green">'samurai'</span><span class="is-black">, </span><span class="is-purple">true</span><span class="is-black">]</span>;</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed a <strong>semicolon</strong> to end the statement</div>
<div class="stab-code"><code class="stabilo">var my_things = [2 + 5, 'samurai', true]<span class="is-black">;</span></code></div>
</div>
</div>
<p>
This means that <code>my_things</code> is equal to <code>[2 + 5, 'samurai', true]</code>.
</p>
<p>
We can now reinstate the <code>alert</code> function:
</p>
<p>
Since we now have <em>two statements</em>, we need to separate them with a <strong>semicolon</strong> <code>;</code> in order to know where one ends and the next one begins.
</p>
{% capture snippet %}{% include snippets/snippet_array_alert.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 19 -->
<div id="step19" class="step">
<div class="content">
{% include partials/gj.html title="Wonderful!" %}
<p>
By storing our array into a variable, we managed to make our code more <strong>readable</strong>.
</p>
<div class="message is-info">
<div class="message-body">
<p>
If you look at other recent tutorials on the Web, you'll see variables defined using the keywords <code>const</code> and <code>let</code>. While they are extremely useful, they're hard for me to explain if you're not familiar with the basics of JavaScript.
</p>
<p>
So that's why I decided to use the keyword <code>var</code> here since it's easier to use and understand when learning JavaScript.
</p>
<p>
If what I just said didn't make sense, don't worry about it and keep on reading :-)
</p>
</div>
</div>
<p>
Although this <code>my_things</code> variable contains a list of several things, we might want to deal with only a <strong>single</strong> item of the list.
</p>
<p>
To access a <em>specific item</em> of an array, you first need to know its <strong>index</strong> (or position) within the array. You then need to wrap this index into <strong>square brackets</strong>.
</p>
<p>
Can you guess which item is gonna be displayed?
</p>
{% capture snippet %}{% include snippets/snippet_array_index.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 20 -->
<div id="step20" class="step">
<div class="content">
{% include partials/gj.html title="You guessed it!" %}
<p>
It's the <strong>second item</strong> that showed up! In programming, indexes start at zero <code>0</code>.
</p>
<div class="stabs is-vertical">
<div class="stab">
<div class="stab-label">you typed the <strong>name</strong> of the array</div>
<div class="stab-code"><code class="stabilo"><span class="is-blue">my_things</span>[1]</code></div>
</div>
<div class="stab">
<div class="stab-label">you opened a <strong>square bracket</strong></div>
<div class="stab-code"><code class="stabilo">my_things<span class="is-black">[</span>1]</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed the <strong>index</strong> of the item you wanted to access</div>
<div class="stab-code"><code class="stabilo">my_things[<span class="is-red">1</span>]</code></div>
</div>
<div class="stab">
<div class="stab-label">you <strong>closed</strong> the square bracket</div>
<div class="stab-code"><code class="stabilo">my_things[1<span class="is-black">]</span></code></div>
</div>
</div>
<p>
It turns out that variables are <strong>objects</strong> too! Which means that variables also have <strong>properties</strong> and <strong>methods</strong>.
</p>
<p>
For example, <code>my_things</code> has a property called <code>length</code>:
</p>
{% capture snippet %}{% include snippets/snippet_array_length.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 21 -->
<div id="step21" class="step">
<div class="content">
{% include partials/gj.html title="That's right!" %}
<p>
The array has <strong>3</strong> items. You'll see that if you add or remove items in <code>my_things</code>, this <code>length</code> value will change accordingly.
</p>
<p>
While readability and properties are useful, the main point of a variable is that it's <strong>editable</strong>: you can change the value afterwards!
</p>
{% capture snippet %}{% include snippets/snippet_array_edit.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 22 -->
<div id="step22" class="step">
<div class="content">
{% include partials/gj.html title="Yep!" %}
<p>
Two alert boxes have been displayed, but with different values! That's because between the first call and the second one, the value of <code>my_things</code> has been <strong>updated</strong>: a fourth item, the string <code>'LOVE'</code>, was added.
</p>
<p>
Note that the second time we're assigning a value to <code>my_things</code>, we're <strong>not</strong> using the <code>var</code> keyword: it's because we're editing the <code>my_things</code> variable defined two lines above.
</p>
<p>
<strong>You only use the keyword <code>var</code> when you're <em>creating</em> a new variable</strong>, not when you're <em>editing</em> one.
</p>
<p>
Do you remember I told you variables had <strong>methods</strong> too (since they're objects)? Another way to edit an array's value is by using the <code>push()</code> method:
</p>
{% capture snippet %}{% include snippets/snippet_array_push.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 23 -->
<div id="step23" class="step">
<div class="content">
{% include partials/gj.html title="Fantastic!" %}
<p>
The <code>my_things</code> array ends up with <strong>4</strong> items.
</p>
<p>
While the <code>push()</code> method altered the array, others simply <strong>return</strong> a value:
</p>
{% capture snippet %}{% include snippets/snippet_array_includes.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 24 -->
<div id="step24" class="step">
<div class="content">
{% include partials/gj.html title="No ninja here!" %}
<p>
The <code>includes()</code> method checked if the string <code>'ninja'</code> was present in the array. Since it wasn't, the method returned <code>false</code>, a <strong>boolean</strong> value.
</p>
<p>
As a matter of fact, when dealing with booleans, typing the keywords <code>true</code> or <code>false</code> is quite rare. Usually, booleans exist as a result of a function call (like <code>includes()</code>) or a <strong>comparison</strong>.
</p>
<p>
Here's a "<em>greater than</em>" comparison:
</p>
{% capture snippet %}{% include snippets/snippet_innerwidth_boolean.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 25 -->
<div id="step25" class="step">
<div class="content">
{% include partials/gj.html title="Great again!" %}
<p>
This means your browser window is <strong id="wider">not</strong> wider than <strong>400 pixels</strong>.
</p>
<div class="stabs">
<div class="stab">
<div class="stab-label">you typed the <strong>first item</strong> to compare, a <strong>number</strong></div>
<div class="stab-code"><code class="stabilo"><span class="is-blue">window<span class="is-black">.</span>innerWidth</span> > 400</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed the "greater than" <strong>operator</strong></div>
<div class="stab-code"><code class="stabilo">window.innerWidth <span class="is-purple">></span> 400</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed the <strong>second item</strong>, also a <strong>number</strong></div>
<div class="stab-code"><code class="stabilo">window.innerWidth > <span class="is-red">400</span></code></div>
</div>
</div>
<p>
Just like the <code>+</code> and <code>*</code> before, <code>></code> is a JavaScript <strong>operator</strong>.
</p>
<p>
When you make such a comparison with the "<em>greater than</em>" operator <code>></code>, you obtain a <strong>boolean</strong> value.
</p>
<p>
Since the result of a <strong>comparison</strong> only has <strong>2</strong> outcomes (<code>true</code> or <code>false</code>), it's useful in cases where your code has to <a onclick="showStep(26);">make a decision</a>…
</p>
</div>
</div>
<!-- 26 -->
<div id="step26" class="step">
<div class="content">
<h2>Conditional statements <span class="stamp is-concept">concept</span></h2>
<p>
Conditional statements are one of the most important concepts in programming. They allow your code to perform certain commands <em>only if</em> certain conditions are met. These conditions can for example be based on:
</p>
<ul>
<li>
a user's input (is the password entered correct?)
</li>
<li>
the current state (is it day or night?)
</li>
<li>
the value of a certain element (is this person older than 18?)
</li>
</ul>
<p>
For now, let's trigger an alert box only if you happen to be on my domain!
</p>
{% capture snippet %}{% include snippets/snippet_if.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
<div class="message is-info">
<div class="message-body">
<p>If you want to <strong>type</strong> this code instead of simply copy-pasting it, press <kbd class="key">Shift</kbd><kbd class="plus">+</kbd><kbd class="key">Enter</kbd> to add line breaks in the console!</p>
</div>
</div>
</div>
</div>
<!-- 27 -->
<div id="step27" class="step">
<div class="content">
{% include partials/gj.html title="Equal indeed!" %}
<p>
We're doing another comparison here, but with the "<em>equal to</em>" operator <code>==</code> instead.
</p>
<div class="stabs is-vertical">
<div class="stab">
<div class="stab-label">you typed the <strong>keyword</strong> <code>if</code></div>
<div class="stab-code"><code class="stabilo"><span class="is-purple">if</span> (window.location.hostname == 'jgthms.com') {</code></div>
</div>
<div class="stab">
<div class="stab-label">you opened a <strong>parenthesis</strong></div>
<div class="stab-code"><code class="stabilo">if <span class="is-black">(</span>window.location.hostname == 'jgthms.com') {</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed a <strong>comparison</strong></div>
<div class="stab-code"><code class="stabilo">if (<span class="is-blue">window</span><span class="is-black">.</span><span class="is-blue">location</span><span class="is-black">.</span><span class="is-blue">hostname</span><span class="is-purple"> == </span><span class="is-green">'jgthms.com'</span>) {</code></div>
</div>
<div class="stab">
<div class="stab-label">you <strong>closed</strong> the parenthesis</div>
<div class="stab-code"><code class="stabilo">if (window.location.hostname == 'jgthms.com'<span class="is-black">)</span> {</code></div>
</div>
<div class="stab">
<div class="stab-label">you opened a <strong>curly bracket</strong></div>
<div class="stab-code"><code class="stabilo">if (window.location.hostname == 'jgthms.com') <span class="is-black">{</span></code></div>
</div>
<div class="stab">
<div class="stab-label">you entered a <strong>block of code</strong> that's only executed if the previous condition is <strong>true</strong></div>
<div class="stab-code"><code class="stabilo"><span class="is-blue"> alert</span><span class="is-black">(</span><span class="is-green">'Welcome on my domain! 🤗'</span><span class="is-black">)</span></code></div>
</div>
<div class="stab">
<div class="stab-label">you <strong>closed</strong> the curly bracket</div>
<div class="stab-code"><code class="stabilo"><span class="is-black">}</span></code></div>
</div>
</div>
<p>
Since the alert box <em>did</em> appear, it means that the <strong>hostname</strong> is indeed <em>equal to</em> <code>'jgthms.com'</code>!
</p>
<p>
We've handled the case when the comparison returns <code>true</code>.
</p>
<p>
To handle the <strong>opposite case</strong>, when the hostname isn't <code>'jgthms.com'</code>, we can use the "<em>not equal to</em>" <strong>operator</strong> <code>!=</code>:
</p>
{% capture snippet %}{% include snippets/snippet_if_not.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet skipRun=true %}
<p>
If you try out this snippet, you'll see that it doesn't trigger anything! (Unless this tutorial has been copied to another domain 😆).
</p>
<p>
What if we wanted to handle both cases <strong>simultaneously</strong>? We could write two <code>if</code> statements in a row. But since one statement is the <em>exact opposite</em> of the other, we can <strong>combine</strong> them with a <code>else</code> statment:
</p>
{% capture snippet %}{% include snippets/snippet_if_else.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 28 -->
<div id="step28" class="step">
<div class="content">
{% include partials/gj.html title="Still equal!" %}
<p>With this conditional setup, we can be sure that:</p>
<ul>
<li><strong>only one</strong> of the two alerts will be triggered, but never both</li>
<li>at least one of the two alerts <em>will</em> be triggered, because we're covering <strong>all</strong> cases</li>
</ul>
<p>
While <code>else</code> is useful for covering all <em>remaining</em> cases, sometimes you want to handle more than two cases.
</p>
<p>
By using <code>else if</code> you can add <strong>intermediate</strong> statements and handle multiple cases:
</p>
{% capture snippet %}{% include snippets/snippet_else_if.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 29 -->
<div id="step29" class="step">
<div class="content">
{% include partials/gj.html title="You got it!" %}
<p>
As soon as one comparison returns <code>true</code>, it will be triggered, and all following statements will be ignored. That's why only one alert box showed up!
</p>
<p>
Conditional statements make use of the <strong>keywords</strong> <code>if</code> and <code>else</code>, followed by a set of <strong>parentheses</strong>.
</p>
<p>
This pattern of keyword/parentheses combination also happens to exist for another <a onclick="showStep(30);">essential programming concept…</a>
</p>
</div>
</div>
<!-- 30 -->
<div id="step30" class="step">
<div class="content">
<h2>Loops <span class="stamp is-concept">concept</span></h2>
<p>
When you want to execute a block of code a <em>certain amount</em> of times, you can use a JavaScript <strong>loop</strong>.
</p>
<p>
Can you guess how many alert boxes this snippet will trigger?
</p>
{% capture snippet %}{% include snippets/snippet_loop.md %}{% endcapture %}
{% include partials/snippet.html contents=snippet %}
</div>
</div>
<!-- 31 -->
<div id="step31" class="step">
<div class="content">
{% include partials/gj.html title="Three it is!" %}
<p>
There were exactly <strong>3</strong> alert boxes! Let's dissect what happened:
</p>
<ul>
<li>
<code>var i = 0</code> is the <strong>initial state</strong><br>
Before the loop even starts, the variable <code>i</code> is assigned a value of zero <code>0</code>.
</li>
<li>
<code>i < 3</code> is the <strong>conditional statement</strong><br>
On every iteration of the loop, we check this comparison.<br>
If it's <code>true</code>, we execute the code in the block.<br>
If it's <code>false</code>, we exit the loop.<br>
</li>
<li>
<code>i++</code> is the <strong>increment expression</strong><br>
<em>If</em> the block of code is executed, this expression is executed.<br>
In this case, the value of <code>i</code> is incremented by 1.
</li>
</ul>
<p>
Here's how you implemented it:
</p>
<div class="stabs is-vertical">
<div class="stab">
<div class="stab-label">you typed the <strong>keyword</strong> <code>for</code></div>
<div class="stab-code"><code class="stabilo"><span class="is-purple">for</span> (var i = 0; i < 3; i++) {</code></div>
</div>
<div class="stab">
<div class="stab-label">you opened a <strong>parenthesis</strong></div>
<div class="stab-code"><code class="stabilo">for <span class="is-black">(</span>var i = 0; i < 3; i++) {</code></div>
</div>
<div class="stab">
<div class="stab-label">you entered the <strong>initial state</strong></div>
<div class="stab-code"><code class="stabilo">for (<span class="is-purple">var </span><span class="is-blue">i</span><span class="is-purple"> = </span><span class="is-red">0</span>; i < 3; i++) {</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed a <strong>semicolon</strong> to separate the expressions</div>
<div class="stab-code"><code class="stabilo">for (var i = 0<span class="is-black">;</span> i < 3; i++) {</code></div>
</div>
<div class="stab">
<div class="stab-label">you entered the <strong>comparison</strong> check</div>
<div class="stab-code"><code class="stabilo">for (var i = 0; <span class="is-blue">i</span><span class="is-purple"> < </span><span class="is-red">3</span>; i++) {</code></div>
</div>
<div class="stab">
<div class="stab-label">you typed a <strong>semicolon</strong> to separate the expressions</div>
<div class="stab-code"><code class="stabilo">for (var i = 0; i < 3<span class="is-black">;</span> i++) {</code></div>
</div>
<div class="stab">
<div class="stab-label">you entered the <strong>increment</strong> expression</div>
<div class="stab-code"><code class="stabilo">for (var i = 0; i < 3; <span class="is-blue">i</span><span class="is-purple">++</span>) {</code></div>
</div>
<div class="stab">
<div class="stab-label">you <strong>closed</strong> the parenthesis</div>
<div class="stab-code"><code class="stabilo">for (var i = 0; i < 3; i++<span class="is-black">)</span> {</code></div>
</div>
<div class="stab">
<div class="stab-label">you opened a <strong>curly bracket</strong></div>
<div class="stab-code"><code class="stabilo">for (var i = 0; i < 3; i++) <span class="is-black">{</span></code></div>
</div>
<div class="stab">
<div class="stab-label">you entered a <strong>block of code</strong> that's only executed if the comparison check is <strong>true</strong></div>
<div class="stab-code"><code class="stabilo"><span class="is-blue"> alert</span><span class="is-black">(</span><span class="is-blue">i</span><span class="is-black">);</span></code></div>
</div>
<div class="stab">
<div class="stab-label">you <strong>closed</strong> the curly bracket</div>
<div class="stab-code"><code class="stabilo"><span class="is-black">}</span></code></div>