JavaScript JJP Presentation

1
JavaScriptJJPPresentation

• Jeff Watson
• Web Internet Programming Group

2
JavaScript Origins

• JavaScript was developed
• by Brendon Eich of Netscape
• in early 1995, who is currently
• the Chief Technology Officer
• of the Mozilla Corporation.
• First called Mocha, named LiveScript to showcase
  the dynamic nature of the scripting language.
• December 4, 1995 - Sun Microsystems and Netscape
  collaborated and renamed LiveScript "JavaScript.
• Possibly named to capitalize on Java, an
  unrelated language which was quickly becoming
  popular with internet developers.

3
Beware of Impostors

• When JavaScript was released in March of 1996,
  Microsoft quickly introduced VBScript (initially
  only worked on Windows PCs), then JScript on July
  16 1996. This was essentially their own version
  of JavaScript, which initially only worked with
  IE 3.0.
• Most JavaScript developers simply checked for
  Netscape, ignoring IE. After Mozilla was
  recognized as a widespread browser, programmers
  created scripts for it, prompting other browsers
  to declare themselves as Mozilla when opening
  these pages, even though they were different
  browsers.
• Netscape wanted standardization and submitted
  JavaScript to ECMA (European Computer
  Manufacturer's Association) which produced the
  ECMA-262 specification in June 1997.
• ECMAScript is often used as a synonym for
  JavaScript and JScript, the two prevailing
  dialects, but Microsoft has stated that JScript
  does NOT conform to ECMA Standards. Said to be
  developed as a compromise between Microsoft and
  Sun, JavaScript creator Brendon Eich was quoted
  as saying that "ECMAScript was always an unwanted
  trade name that sounds like a skin disease."

4
Revisions

• The ECMA standard has released 2 revisions after
  the initial release, with a third in the works.
• Edition 2 added small revisions to conform to
  ISO/IEC standards.
• The third edition added regular expressions,
  better string handling, new control statements,
  try/catch exception handling, tighter definition
  of errors, formatting for numeric output and
  other enhancements.
• The fourth edition will correspond to JavaScript
  2.0, and introduce classes, structural types,
  packages and namespaces, static typing,
  generators and iterators, algebraic data types
  and other small additions.

5
JavaScript is NOT Java

• There are several main differences
• Java is used to create standalone applications,
  while JavaScript is text which needs to be
  embedded into HTML.
• Java is a much larger and more complicated
  language, with many more built-in functions and
  objects, as well as several libraries to support
  it. JavaScript is a much smaller set of built-in
  functions and objects used for simple internet
  applications.
• Java is strongly typed (type-checking at
  compilation, JavaScript is dynamically typed
  (type-checking performed at run-time).
• Array indices are not checked for validity
  (required in Java).
• Although it supports instances of ADTs (objects),
  JavaScript does not support inheritance nor
  dynamic binding of method calls to methods, so it
  is not a true object-oriented language.
• Java doesnt have global functions due to OOP
  limitations, while they are used regularly in
  JavaScript code.

6
Functionality

• The first main draw for JavaScript was the
  incorporation of images properties, such as being
  able to click on various parts of an image with
  varying results.
• The other main feature was that JavaScript could
  easily spawn new windows, enabling new
  information to be presented without navigating
  away from the main page. This caused many
  annoying pop-up ads when the internet was
  becoming popular in the United States.
• JavaScript is embedded directly into HTML, and
  enables programmers to put static control
  structures as well as dynamic code into web
  pages.
• The scripts would be run on the clients machine
  rather than a server so that valuable information
  on the server could be more easily protected.
• JavaScript works easily with HTML forms as well
  as alongside several other internet programming
  languages, and it is a simple way to accept and
  manipulate user input.

7
Dynamic Features

• Types are associated with values, not variables.
  Variables can be bound to several types of values
  throughout the course of a script.
• Objects are instantiated as associative arrays,
  which lets programmers bind methods and variables
  to them whenever they decide it is necessary.
• JavaScript is interpreted, not compiled. The only
  way to test code is by running it, and this is
  the only time that errors can be detected as
  well.
• Although there are debuggers available, virtually
  all of them only work with the JavaScript code
  and since the script code works within HTML and
  alongside other languages, debugging can be very
  problematic.

8
JavaScript vs. C

• JavaScript is object-based, which is a limited
  version of an object oriented language, mainly
  due to its lack of inheritance and its
  prototype-based object handling.
• JavaScript object properties can be added at any
  time and do not need to be pre-defined in an
  object declaration or constructor.
• JavaScript does not support block-scoping, only
  global and function scoping.
• JavaScript uses prototypes rather than classes.
  While they are not the same thing, it enables
  programmers to do many operations that are
  comparable to working with classes.
• JavaScript relies on other applications,
  specifically a JavaScript-enabled web browser to
  run properly.

9
Embedding JavaScript in HTML
Embedding JavaScript into HTML is simple, and
since JavaScript code is self-contained in
ltscriptgt tags it allows for code from other
languages and forms to be included in the page as
well.
10
Functions in JavaScript

• Built-in functions are almost completely
  concerned with validating argument types which
  are commonly passed into functions or methods as
  well as converting variables to and from these
  types.
• This includes specifics such as NaN(),
  infinity(), and undefined(), as well as functions
  for encoding and decoding data.
• Functions can be created through several
  different techniques, and since JavaScript uses
  first-class functions, they are treated as
  objects.
• Function objects have properties, and can be
  passed around and used just like any other
  object.
• Functions can be declared within other functions.
  These are called inner functions and are the
  main idea behind closures in JavaScript.

11
Function Declaration Example
JavaScript has many different techniques for
creating functions, and these show the objective
nature that functions take on in the language.
12
Closures

• An expression (typically a function) that can
  have free variables together with an environment
  that binds those variables (that "closes" the
  expression).
• This generally happens when a function contains
  another function inside it, and has access to the
  outer function's variables. If the outer function
  returns and the inner function is still
  accessible to outside code, the inner function
  still has access to the outer function's
  variables.
• This can result in security issues in some cases,
  but also has some practical applications.

13
Closure Example
The function getSecret() is declared within
Guard(), which returns a reference to function
getSecret(). This gives outside code access to an
internal function, in turn giving the outside
code access to the variables used within the
inner function which, in this case, belong to
function Guard().
Output (Along with a blank page)
14
Built-in Objects

• JavaScripts collection of built-in objects is
  relatively small compared to other languages, but
  still provides the basic objects needed for most
  functional programming.
• This includes mathematical objects, date/time
  objects and objective arrays.
• Each type of built-in object is supported with
  several methods used to manipulate and display
  the data associated with them.
• As stated before, JavaScript functions themselves
  are objects, and there are some other surprising
  objects such as strings and numbers which many
  programmers are used to seeing within built-in
  data types. This allows for elaborate string and
  number manipulation.

15
Forms and JavaScript
It is easy to utilize JavaScript in HTML forms,
it adds functionality as well as plenty of ways
to transfer and manipulate data.
16
JavaScript allows HTML forms to be more dynamic
in ways such as providing a simple means to
manipulate and display input in an environment
familiar to the modern programmer.
17
Pop-Up Window Creation
JavaScripts popularity grew very quickly once
advertisers realized that they could spawn
windows with client-side code, resulting in
massive amounts of pop-up advertisements,
especially during early development of the
language. Of course, spawning windows has very
many practical uses as well.
18
Window Creation/Manipulation Code
See? Easy.
19
Menus and Rollover
JavaScript is able to recognize where images are
clicked and can provide different procedures for
different areas and images, providing an easy way
to create internet menus.
20
Rollover Illustrated
The buttons darken as the mouse rolls over them,
this helps to show users which objects are
clickable and/or lead to links. Button A will
link to http//www.google.com and Button 2 will
link to http//www.yahoo.com.
21
Current Usage

• JavaScript has now become commonplace when
  creating online forms, buttons, menus, and other
  input methods, as well as ways to validate input.
  This is the dynamic nature of JavaScript.
• Developers like JavaScript because it is easy to
  learn and keeps virtually all code executing on
  the clients side, preventing security issues
  present in other internet languages.
• Also, almost every web browser in the industry
  has developed a JavaScript debugger due to its
  growing popularity.
• Future development will include the inclusion of
  classes and even more built-in functionality, and
  JavaScript 2.0 will provide developers with a
  myriad of new internet programming techniques.

22
References

• http//en.wikipedia.org/wiki/JavaScript
• Sebesta, Programming Languages. 8th Edition.
• JavaScript with DOM Scripting and Ajax