LLC-JavaScript/js_objects.html at master · pearlchen/LLC-JavaScript · GitHub

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<!DOCTYPE html>
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<title>Ladies Learning Code - JavaScript March 18, 2012</title>
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<divid="presentation">
<!-- **************************************** -->

<articleclass='slide slide-subhead'>
<h1>JavaScript Part 4</h1>
<p>Objects</p>
</article>

<!-- SLIDE: -->
<articleclass='slide slide-list'>
<h2>Objects</h2>
<p>If variables are boxes, OBJECTS can be thought of as bento boxes -- &quot;advanced variables&quot; if you will.</p>
<pclass="centered"><imgsrc="assets/bento_box_real.jpg" height="400" alt="A Real Bento Box" /></p>
</article>

<!-- SLIDE: -->
<articleclass='slide slide-list'>
<h3>How Bento Boxes are like Objects</h3>
<br><br><br><br>
<tablewidth="100%">
<tr>
<tdclass="centered">
<imgsrc="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>
<preclass="prettyprint">var takeout = "Fried Rice";</pre>
</td>
</tr>
<tr>
<tdwidth="430" align="center" valign="middle">
<imgsrc="assets/BentoBox.png" width="339" height="207" alt="Bento Box diagram" />
</td>
<td>
<p>An object holds a collection of values.</p>
<preclass="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: -->
<articleclass='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>
<pclass="centered highlight"><code>var bentobox = <spanclass="assignment">{}</span>;</code></p>
<pclass="centered sidenote">Yes, it's weird but think about the {} as a sort of funky container.</p>
</article>
<!-- SLIDE: -->
<articleclass='slide slide-list'>
<h2>Object Properties</h2>
<p>The &quot;compartments&quot; of objects are called <spanclass="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>

<tablewidth="100%" style="font-size: 24px;">
<tr>
<tdwidth="42%">
<strong>Dot notation:</strong><br>
<code>myObject.property = value;</code>
<br><br>
<preclass="prettyprint">
bentobox.main = "Teriyaki";
bentobox.side = "Tempura";
</pre>
</td>
<tdwidth="8%"></td>
<tdwidth="50%">
<strong>Key-Value Lookup:</strong><br>
<code>myObject[key] = value;</code>
<br>
<br>
<preclass="prettyprint">
bentobox["main"] = "Teriyaki";
bentobox["side"] = "Tempura";
</pre>

<spanclass="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>
<preclass="prettyprint">
bentobox.soup0 = "Miso";
bentobox.soup1 = "Udon";</pre>
</td>
<td></td>
<td>
<preclass="prettyprint">
bentobox["soup"+1] = "Miso";
bentobox["soup"+2] = "Udon";
</pre></td>
</tr>
</table>
<br><br><br>
<pclass="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: -->
<articleclass='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>
<tablewidth="100%">
<tr>
<tdclass="centered"><imgsrc="assets/BentoBox.png" width="339" height="207" alt="Bento box variation #1" /></td>
<tdclass="centered"><imgsrc="assets/BentoBox2.png" width="339" height="207" alt="Bento box variation #2" /></td>
</tr>
</table>
</article>

<!-- SLIDE: -->
<articleclass='slide slide-list'>
<h2>Think of Everything as an Object*</h2>
<p>When I said that objects were &quot;advanced variables&quot;, here's another way of looking at it:</p>
<pclass="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>
<divclass="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>
<pclass="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: -->
<articleclass='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>
<textareaclass='coder-editor'>SCRIPT

var firstName = "Pearl";

var numLetters = firstName.length;
document.write( "numLetters: " +
 numLetters );

SCRIPTEND</textarea>
</article>

<!-- SLIDE: -->
<articleclass='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>
<tablewidth="100%" style="font-size: 24px;">
<tr>
<tdwidth="40%">
<strong>This function...</strong>
<preclass="prettyprint">
function sayHello(){
 document.write("hello");
}

sayHello();
</pre>
</td>
<tdwidth="5%" align="center"><br>
<br><br>
 ➞
</td>
<td>
<strong>is the same as:</strong>
<preclass="prettyprint">
sayHello = function() {
 document.write("hello");
}

sayHello();
</pre>
</td>
</tr>
<tr>
<td>
</td>
<td>
</td>
<tdalign="center">ↆ</td>
</tr>
<tr>
<td>
</td>
<td>
</td>
<td>
<strong>But now look at this!</strong>
<preclass="prettyprint">
var welcomeTeam = {};
welcomeTeam.sayHello = function() {
 document.write("hello");
}
welcomeTeam.sayHello();
</pre>
</td>
</tr>
</table>
</article>

<!-- SLIDE: -->
<articleclass='slide slide-list'>
<h3>Object Methods</h3>
<p>When a function is associated with an object we call it a <spanclass="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>
<textareaclass='coder-editor'>
<script>

varsalePrice1=20.00*0.50;
varsalePrice2=35.00*0.50;
varsalePrice3=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>
<scripttype="coder-solution">SCRIPT

varsalePrice1=20.00*0.50;
varsalePrice2=35.00*0.50;
varsalePrice3=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: -->
<articleclass='slide slide-list'>
<h3>Object Methods</h3>
<p>Here's another <spanclass="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>
<textareaclass='coder-editor coder-editor-full'>
<script>

varemailTemplate="Dear [First Name], thank you for subscribing.";

// uh-oh, let's make this more personal
document.write(emailTemplate);

</script></textarea>
<scripttype="coder-solution">SCRIPT

varemailTemplate="Dear [First Name], thank you for subscribing.";

// uh-oh, let's make this more personal
varemailFinal=emailTemplate.replace("[First Name]","Pearl")
document.write(emailFinal);

SCRIPTEND</script>

</article>

<!-- SLIDE: -->
<articleclass='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: <ahref="http://www.scribd.com/doc/19457597/Javascript-Methods" target="_blank">http://www.scribd.com/doc/19457597/Javascript-Methods</a>.</p>
<p>Or this cheatsheet: <ahref="http://www.addedbytes.com/download/javascript-cheat-sheet-v1/png/" target="_blank">http://www.addedbytes.com/download/javascript-cheat-sheet-v1/png</a>.</p>
</article>

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