Intro to JavaScript

Introduction to JavaScript
Learn how to program your computer!

0
You can and must
understand computers
NOW

“ Everything is deeply intertwingled. In an
important sense there are no “subjects” at all;
there is only all knowledge, since the cross-
connections among the myriad topics of this
world simply cannot be divided up neatly.”

—Ted Nelson, Computer Lib/Dream Machines

“ When human beings acquired language, we
learned not just how to listen but how to speak.
When we gained literacy, we learned not just how
to read but how to write. And as we move into an
increasingly digital reality, we must learn not just
how to use programs but how to make them.”

—Douglas Rushkoff, Program or Be Programmed

“ The single most significant change in the politics
of cyberspace is the coming of age of this simple
idea: The code is law. The architectures of
cyberspace are as important as the law in defining
and defeating the liberties of the Net.”

—Lawrence Lessig, The Code Is the Law

Programming is very
careful typing

Programming is
figuring out why it
broke

Programming in general

• A series of text files that get compiled
and executed

• Code is “digested,” going from human-
readable to a hardware-ready form

• Ultimately programs run as assembly,
low-level instructions for your CPU

JavaScript in particular

• Increasingly the web page scripting
language

• Most likely the widest deployed
runtime

• JavaScript has nothing to do with
Java, except some syntax similarities

Lines of code

• A line of code is a basic unit of
programming

• Tells the computer to do something
• Sometimes a “line” of code can span
more than one line

A simple line of code

alert("Hello, world!");

Let’s try this using
Firebug

Compilers are unforgiving

• The computer cuts you no slack
• All code is subject to bugs
• The error console is your friend
• Debugging is about identifying,
characterizing, and resolving
problems



Function name



Function name Parentheses call the function




Function argument (a string)




Function argument (a string)

Designates the end of the line

The variable metaphor

“Variables are like a box
you can put data into.”

Variables

• Variables store data for future use
• var x = y; is how you assign a new
variable in JavaScript

• We can now refer to x in future lines
of code, and know it means y

Variables (boolean type)

• var x = true; is how you assign a new

of code, and know it means true

Variables (boolean type)

• var x = false; is how you assign a new

of code, and know it means false

Variables (numeric type)

• var x = 47; is how you assign a new

of code, and know it means 47

Variables (string type)

• var x = "pony"; is how you assign a
new variable in JavaScript

of code, and know it means pony.

Variable logic

// What is the value of z?
var x = 3;
var y = x + 1;
var z = y;

Multiple lines of code

var msg = "Hello, world!";
var func = alert;
func(msg);

Designate the ends of the lines


var func = alert;
func(msg);

The first line stores a string


var func = alert;
func(msg);

The second line stores a function


var func = alert;
func(msg);

The third line executes the
stored function with the string

Commenting code

// First we store the message

// Next, we choose a function to call
var func = alert;

// Finally, we combine the two
func(msg);

Commenting code

/*

This code demonstrates the standard
Hello World program, over three lines
instead of just one.

*/
var func = alert;
func(msg);

Creating a new function

// Outputs a simple message
function output_message() {
var func = alert;
func(msg);
}

Calling our function

function output_message() {
var func = alert;
func(msg);
}

output_message();

Arguments

function output_message(msg) {
var func = alert;
func(msg);
}

output_message("Hello, world!");
output_message("¡Hola, mundo!");

JavaScript on the web

<script>

// JavaScript code is typically embedded in HTML
// <script> tags

</script>

HTML + JavaScript
<html>
<head>
<title>HTML + JavaScript</title>
</head>
<body>
<p>Stuff *on* the page goes up here.</p>
<script>

// JavaScript code that modifies the page should
// go below everything else in the <body>.

</script>
</body>
</html>

Hide content
<html>
<head>
<title>Hide content</title>
</head>
<body>
<p id="hide">Click to hide me!</p>
<script src="mootools.js"></script>
<script>
$('hide').addEvent('click', function() {
$('hide').fade('out');
});
</script>
</body>
</html>

HTML + CSS + JavaScript
<html>
<head>
<title>HTML + CSS + JavaScript</title>
<style>
#content {
background: #000;
}
</style>
</head>
<body>
<p id="content">Hello, world!</p>
<script>
var content = document.getElementById('content');
content.style.color = '#fff';
</script>
</body>
</html>

HTML + CSS + JavaScript

<html>
<head>
<title>HTML + CSS + JavaScript</title>
<link rel="stylesheet" href="styles.css" />
</head>
<body>
<p>
Separating code into .js and .css files is a
good way to keep things tidy.
</p>
<script src="scripts.js"></script>
</body>
</html>

Slide show HTML
<html>
<head>
<title>Slide show</title>
<link rel="stylesheet" href="styles.css" />
</head>
<body>
<div id="slides">
<div id="inner">
<img src="images/1.jpg" />
</div>
</div>
<script src="mootools.js"></script>
<script src="script.js"></script>
</body>
</html>

Slide show CSS
#slides {
width: 991px;
height: 671px;
margin: 0 auto;
overflow: hidden;
position: relative;
}

#inner {
position: absolute;
left: 0;
top: 0;
}

#slides img {
float: left;
}

Slide show JavaScript

var width = 991;
var n = 0;
var count = $$('#slides img').length;

$('slides').addEvent('click', function() {
n = (n + 1) % count; // Increment
$('inner').tween('left', n * -width);
});

Take your time, it
won’t come quickly

Resources
• Eloquent JavaScript • _why’s poignant
guide to Ruby
• MooTorial
• Dive into Python
• w3schools.com
• Visual Quickstart
• Mozilla devmo Guide

• WebMonkey • Lynda tutorials

• The Rhino Book

http://www.vimeo.com/5047563

Intro to JavaScript

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