JavaScript
Jonathan Vinson
CSC 415
History
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Developed in 1995 by Brendan Eich (Netscape)
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Created in 10 days
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Originally called Mocha, then LiveScript
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Trademarked by Sun and became JavaScript
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Officially called ECMAScript since it was
standardized by EMCA in 1996
Now on ECMAScript 5
Names

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Must begin with a letter, $, or _
Can contain letters, digits, underscores, and
dollar signs
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Case sensitive
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Reserved words cannot be used as names
Scope
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Static scoped
Variables declared within a JavaScript function
are local to that function
Variables declared outside of a function have
global scope
Assigning a value to a variable that hasn't yet
been declared will automatically make that
variable global
Data Types
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Dynamic Data Types

Number
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String
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Boolean
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Array
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Object

Undefined
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Empty
Operators
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+, -, *, /, %, ++, --
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==, ===, !=, !==, >, <, >=, <=
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&&, ||, !
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&, |, ~, ^, <<, >>
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typeof, delete, unary +

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Strings can use arithmetic operators to interact
with other strings and numbers
Unary + operator converts a string to an integer
Statements

=, +=, -=, *=, /=, %=
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While
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Do … while
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For
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For … in
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If … else

Control: continue, break
Subprograms

Functions are used in JavaScript
function myFunction(p1, p2) {
return p1 * p2;
}
Exception Handling

Try, Catch, Throw, and Finally
try {
if(x == "") throw "Empty";
if(isNaN(x)) throw "Not a number";
if(x > 10) throw "Too high";
if(x < 5) throw "Too low";
}
catch(err) {
message.innerHTML = "Error: " + err + ".";
}
finally {
document.getElementById("demo").value = "";
}
Event Handling

Handles HTML events
<button onclick="displayDate()">The time is?</button>
Libraries of JavaScript

Prototype

MooTools
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jQuery
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YUI
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Ext JS
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Dojo

UIZE
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Many More!
jQuery

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Most popular JavaScript framework on the
internet today
Uses CSS selectors to access and manipulate
HTML elements (DOM Objects)
Provides companion UI framework and many
other plug-ins
Used by Google, Microsoft, IBM, and Netflix
jQuery
jQuery
$ (‘body’) .css (‘background’, ‘#ccc’);
JavaScript
Function changeBachground(color) {
Document.body.style.background = color;
}
Prototype



Provides a simple API to perform common web
tasks
API is short for Application Programming
Interface, and is a library for manipulating the
HTML DOM
Prototype enhances JavaScript by providing
classes and inheritance
Mootools

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Also a framework that offers an API to make
common JavaScript programming easier
Includes some lightweight effects and animation
functions
Content Delivery Networks

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Speed is always important with web pages
Many web sites use the same JavaScript
framework
CDNs solve this by providing a network of
servers containing shared code libraries
Google provides a free CDN for many
JavaScript libraries including: jQuery, Prototype,
Mootools, Dojo, and Yahoo! YUI
Other Useful Features

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AJAX (Asynhronous JavaScript and XML)

A way to exchange data with a server, and
update parts of a web page without reloading
the whole page

https://www.youtube.com/watch?v=m1o7TxX9
aBg
JSON (JavaScript Object Notation)

A lightweight data interchange format that is
language independent, and easy to
understand.
Readability

Familiar Syntax
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Simple
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Easy to read
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Libraries such as jQuery can make reading
JavaScript much more condensed
Writability

Allows for expressive coding
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Familiar Syntax
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Easy to pick up
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Development is relatively fast
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Frameworks allow for quick building of
JavaScript files
Reliability

Widely supported
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Standardized
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Run with client resources
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Many great libraries
Cost
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Training is cheap
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Free IDEs
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Very portable
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Easily maintainable
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Most libraries are also free