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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Ladies Learning Code - Intro to JavaScript</title>
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<div id="presentation">
<!-- **************************************** -->
<article class='slide slide-subhead'>
<h1>JavaScript Part 4</h1>
<p>Objects</p>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h2>Objects</h2>
<p>If variables are boxes, OBJECTS can be thought of as bento boxes -- "advanced variables" if you will.</p>
<p class="centered"><img src="assets/bento_box_real.jpg" height="400" alt="A Real Bento Box" /></p>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h3>How Bento Boxes are like Objects</h3>
<br><br><br><br>
<table width="100%">
<tr>
<td class="centered">
<img src="assets/Rice.png" width="193" height="119" alt="Rice box diagram" />
<br><br><br>
</td>
<td>
<p>A basic variable only holds one value.</p>
<pre class="prettyprint">var takeout = "Fried Rice";</pre>
</td>
</tr>
<tr>
<td width="430" align="center" valign="middle">
<img src="assets/BentoBox.png" width="339" height="207" alt="Bento Box diagram" />
</td>
<td>
<p>An object holds a collection of values.</p>
<pre class="prettyprint">// create a new object
var bentobox = {};
// fill it with stuff
bentobox.main = "Teriyaki";
bentobox.side = "Tempura";
bentobox.salad = "Seaweed Salad";
bentobox.soup = "Miso";
bentobox.sauce = "Soya";
bentobox.dessert = "Fruit";</pre>
</td>
</tr>
</table>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h2>Creating an Object</h2>
<p>Creating an object is easy. Just like any other variable, use the <strong><code>var</code></strong> keyword and give it a descriptive name. </p>
<p>But instead of assigning a single value right away, use these curly braces to make an empty object.</p>
<p class="centered highlight"><code>var bentobox = <span class="assignment">{}</span>;</code></p>
<p class="centered sidenote">Yes, it's weird but think about the {} as a sort of funky container.</p>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h2>Object Properties</h2>
<p>The "compartments" of objects are called <span class="keyword">PROPERTIES</span>.</p>
<p>If you already have an existing object, there are a few ways to access and set a value to a property. Since these two are very commonly used, they will both be discussed.</p>
<table width="100%" style="font-size: 24px;">
<tr>
<td width="42%">
<strong>Dot notation:</strong><br>
<code>myObject.property = value;</code>
<br><br>
<pre class="prettyprint">
bentobox.main = "Teriyaki";
bentobox.side = "Tempura";
</pre>
</td>
<td width="8%"></td>
<td width="50%">
<strong>Key-Value Lookup:</strong><br>
<code>myObject[key] = value;</code>
<br>
<br>
<pre class="prettyprint">
bentobox["main"] = "Teriyaki";
bentobox["side"] = "Tempura";
</pre>
<span class="sidenote">This will be most useful after you understand arrays. <strong>Advantage</strong>:
You can use concatenation with the key string in order to do look up something that's partially dynamic:</span>
</td>
</tr>
<tr>
<td>
<pre class="prettyprint">
bentobox.soup0 = "Miso";
bentobox.soup1 = "Udon";</pre>
</td>
<td></td>
<td>
<pre class="prettyprint">
bentobox["soup"+1] = "Miso";
bentobox["soup"+2] = "Udon";
</pre></td>
</tr>
</table>
<br><br><br>
<p class="sidenote"><strong>Advanced sidenote: </strong><br>
Alternatively, you can both declare an object and set it's values at the <strong>same</strong> time: <br>
<code>var bentobox = { soup:"Miso", main:"Teriyaki" };</code></p>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h2>Why use Objects?</h2>
<p><em>Advanced topic:</em> Objects are useful because you group all these properties together and you can <strong>reuse</strong> the object over again.</p>
<p>There's an <strong>expectation</strong> of what you'll get in a bento box. <br>
<br>
Some items are <strong>fixed</strong> (a fruit dessert, a miso soup) but some compartments can be <strong>edited</strong> (a gyoza side versus tempura). </p>
<table width="100%">
<tr>
<td class="centered"><img src="assets/BentoBox.png" width="339" height="207" alt="Bento box variation #1" /></td>
<td class="centered"><img src="assets/BentoBox2.png" width="339" height="207" alt="Bento box variation #2" /></td>
</tr>
</table>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h2>Think of Everything as an Object*</h2>
<p>When I said that objects were "advanced variables", here's another way of looking at it:</p>
<p class="centered"><strong>All JavaScript variables can be treated like objects too.</strong></p>
<div>
<p>If curly braces are a container for a generic object, quotes are containers for characters. When we get to arrays next, you'll see that it uses square brackets. (The only "uncontainered" object we've introduced today was a number.)</p>
</div>
<div class="reminders">
<pre>var stringObject = “ ”;
var arrayObject = [ ];</pre>
</div>
<p>Some objects are simpler than others but almost everything in JavaScript has properties available to us.</p>
<p class="sidenote">*Again, I need to oversimplify. The concept called DATA TYPE is a hairy topic. For more info: http://javascriptweblog.wordpress.com/2010/09/27/the-secret-life-of-javascript-primitives/ and http://www.2ality.com/2011/03/javascript-values-not-everything-is.html</p>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h2>Built-in JavaScript Properties</h2>
<p>In this workshop we won't be creating any of our own objects but JavaScript already has many objects built into the language.</p>
<p>Let's look at a string object and the <code>length</code> property which returns the number of characters in a string. Try putting your own name in here.</p>
<textarea class='coder-editor'>SCRIPT
var firstName = "Your Name";
var numLetters = firstName.length;
document.write( "numLetters: " +
numLetters );
SCRIPTEND</textarea>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h2>Functions in Objects</h2>
<p>Previously, we talked about functions as blocks of re-usable code. This might sound crazy but <strong>you can store functions in variables</strong> too!</p>
<table width="100%" style="font-size: 24px;">
<tr>
<td width="40%">
<strong>This function...</strong>
<pre class="prettyprint">
function sayHello(){
document.write("hello");
}
sayHello();
</pre>
</td>
<td width="5%" align="center"><br>
<br><br>
➞
</td>
<td>
<strong>is the same as:</strong>
<pre class="prettyprint">
sayHello = function() {
document.write("hello");
}
sayHello();
</pre>
</td>
</tr>
<tr>
<td>
</td>
<td>
</td>
<td align="center">ↆ</td>
</tr>
<tr>
<td>
</td>
<td>
</td>
<td>
<strong>But now look at this!</strong>
<pre class="prettyprint">
var welcomeTeam = {};
welcomeTeam.sayHello = function() {
document.write("hello");
}
welcomeTeam.sayHello();
</pre>
</td>
</tr>
</table>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h3>Object Methods</h3>
<p>When a function is associated with an object we call it a <span class="keyword">METHOD</span>.</p>
<p>Let's say you're having a robot sale! Everything is 50% off. But, after doing the math, you notice that the sale price is a bit off.. Let's declare a sale price and manipulate it using <code>toFixed()</code>. When you use a method, it gives you access to all the hard work that someone else did and it only takes you one line to use it!</p>
<textarea class='coder-editor'>
<script>
var salePrice1 = 20.00 * 0.50;
var salePrice2 = 35.00 * 0.50;
var salePrice3 = 25.99 * 0.50;
// uh-oh, can we make sure we
// always see 2 decimal spaces?
document.write( salePrice1 );
document.write( "<br />" );
document.write( salePrice2 );
document.write( "<br />" );
document.write( salePrice3 );
</script></textarea>
<script type="coder-solution">SCRIPT
var salePrice1 = 20.00 * 0.50;
var salePrice2 = 35.00 * 0.50;
var salePrice3 = 25.99 * 0.50;
// uh-oh, can we make sure we
// always see 2 decimal spaces?
document.write( salePrice1.toFixed(2) );
document.write( "<br />" );
document.write( salePrice2.toFixed(2) );
document.write( "<br />" );
document.write( salePrice3.toFixed(2) );
SCRIPTEND</script>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h3>Object Methods</h3>
<p>Here's another <span class="keyword">METHOD</span> associated with strings.</p>
<p>Have you ever created an email newsletter? You usually have a template but you want to replace <code>[First Name]</code> with someone's actual name. Use <code>.replace()</code> for that!</p>
<textarea class='coder-editor coder-editor-full'>
<script>
var emailTemplate = "Dear [First Name], thank you for subscribing.";
// uh-oh, let's make this more personal
document.write( emailTemplate );
</script></textarea>
<script type="coder-solution">SCRIPT
var emailTemplate = "Dear [First Name], thank you for subscribing.";
// uh-oh, let's make this more personal
var emailFinal = emailTemplate.replace("[First Name]", "Your Name");
document.write( emailFinal );
SCRIPTEND</script>
</article>
<!-- SLIDE: -->
<article class='slide slide-list'>
<h2>Looking up properties and references</h2>
<p><code>length</code> and <code>toFixed()</code> are only two of many (many!) more built-in properties and methods of objects in JavaScript.</p>
<p>Check out this list: <a href="http://www.scribd.com/doc/19457597/Javascript-Methods" target="_blank">http://www.scribd.com/doc/19457597/Javascript-Methods</a>.</p>
<p>Or this cheatsheet: <a href="http://www.cheatography.com/davechild/cheat-sheets/javascript/" target="_blank">http://www.cheatography.com/davechild/cheat-sheets/javascript/</a>.</p>
</article>
<!-- SLIDE: Next section -->
<article class='slide slide-list'>
<p class="centered vertically_centered"><a href="js_dom.html"><img src="assets/next_section_icon.gif" width="230" height="70" alt="Click to go to next section" /></a></p>
</article>
<!-- **************************************** -->
</div>
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