Java is:
Object Oriented: In Java, everything is an Object. Java
can be easily extended since it is based on the Object model.
Platform independent: Unlike many other programming
languages including C and C++, when Java is compiled, it is not compiled
into platform specific machine, rather into platform independent byte
code. This byte code is distributed over the web and interpreted by
virtual Machine (JVM) on whichever platform it is being run.
JavaScript in <body>
In this example, JavaScript writes into the HTML <body>
while the page loads:
Example
<!DOCTYPE html>
<html>
<body>
.
.
<script>
document.write("<h1>This is a heading</h1>");
document.write("<p>This is a paragraph</p>");
</script>
.
.
</body>
</html>
JavaScript Functions and Events
The JavaScript statements, in the example above, are
executed while the page loads.
More often, we want to execute code when
an event occurs, like when the user clicks a button.
If we put JavaScript code inside a function, we can
call that function when an event occurs.
You will learn much more about JavaScript functions and
events in later chapters.
A JavaScript Function in <head>
In this example, a JavaScript function is placed in the
<head> section of an HTML page.
The function is called when a button is clicked:
Example
<!DOCTYPE html>
<html>
<head>
<script>
function myFunction()
{
document.getElementById("demo").innerHTML="My First JavaScript
Function";
}
</script>
</head>
<body>
<h1>My Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try
it</button>
</body>
</html>
A JavaScript Function in <body>
In this example, a JavaScript function is placed in the
<body> section of an HTML page.
The function is called when a button is clicked:
Example
<!DOCTYPE html>
<html>
<body>
<h1>My Web Page</h1>
<p id="demo">A Paragraph</p>
<button type="button" onclick="myFunction()">Try
it</button>
<script>
function myFunction()
{
document.getElementById("demo").innerHTML="My First JavaScript
Function";
}
</script>
</body>
</html>
External JavaScripts
Scripts can also be placed in external files. External
files often contain code to be used by several different web pages.
External JavaScript files have the file extension .js.
To use an external script, point to the .js file in the
"src" attribute of the <script> tag:
Example
<!DOCTYPE html>
<html>
<body>
<script src="myScript.js"></script>
</body>
</html>
you can place the script in the <head> or <body> as you
like. The script will behave as if it was located exactly where you put
the <script> tag in the document.
