JavaScript
2018/19 COMP3322A Modern Technologies on WWW
Contents
•
JavaScript and its history
•
Adding JavaScript
•
The JavaScript language
•
JavaScript Objects
•
The Document Object Model (DOM)
•
Events
•
Form Validation
Client-Side Scripting
•
Let the client compute
What is JavaScript
•
JavaScript runs right inside the browser.
•
JavaScript is dynamically typed.
•
JavaScript is object-oriented in that almost everything in the
language is an object
•
the objects in JavaScript are prototype-based rather than class-based, which
means that while JavaScript shares some syntactic features of PHP, Java or
C#, it is also quite different from those languages.
JavaScript isn’t related to Java
•
Although it contains the word
Java
, JavaScript and Java are vastly
different programming languages with different uses. Java is a full-
fledged compiled, object-oriented language, popular for its ability
to run on any platform with a JVM installed.
•
Conversely, JavaScript is one of the world’s most popular
languages, with fewer of the object-oriented features of Java, and
runs directly inside the browser, without the need for the JVM.
JavaScript History
•
JavaScript was introduced by Netscape in their Navigator browser back
in 1995.
•
JavaScript is in fact an implementation of a standardized scripting
language called
ECMAScript
•
IN 1998, ECMAScript 2 was released.
•
In 1999, ECMAScript 3 was released.
•
Which evolved into what is today’s modern JavaScript.
•
ECMAScript 5 was released in 2009.
•
At the moment, ECMAScript 2018 (the 9
th
edition) is the latest release.
Source: Wikipedia ECMAScript
Where does JavaScript go?
•
JavaScript can be linked to an HTML page in a number of ways.
•
Inline
•
Embedded in the document
•
Link to an external file
•
When the browser encounters a block of JavaScript, it generally
runs it in order, from top to bottom. This means that you need to be
careful what order you put things in.
Inline JavaScript
•
Inline JavaScript refers to add the JavaScript code directly within
certain HTML attributes.
•
Inline JavaScript is a real maintenance nightmare.
<a href=
"JavaScript:OpenWindow();">more info<
/a>
<input type=
"button" onclick="alert('Are you sure?');">
Embedded JavaScript
•
Embedded JavaScript refers to the practice of placing JavaScript
code within a <script> element.
•
You can place any number of scripts in an HTML document.
•
Scripts can be placed in the <body>, or in the <head> section of an
HTML page, or in both.
<
script
>
function
myFunction() {
document.getElementById(
"demo"
).innerHTML =
"Paragraph changed."
;
}
<
/script
>
External JavaScript
•
JavaScript supports this separation by allowing links to an external
file that contains the JavaScript.
•
By convention, JavaScript external files have the extension .js.
