Basics of JavaScript

What is JavaScript?

JavaScript is a computer language
A computer language is a series of instructions that instruct the computer to do something
JavaScript is not the script version of the Java language.

The most common uses of JavaScript are interacting with users, getting information from them, and validating their actions.
JavaScript can also be used for various "tricks" like rollover images
A mortgage seller's website that has a JavaScript-driven mortgage calculator

All that you need is a simple text editor, such as Windows NotePad
When it comes to learning the basics, it's often best to write the code by hand rather than relying on a tool to do it for you.
You'll also need a browser to view your web pages in.

Inserting JavaScript in a web page is much like inserting any other HTML content; we use tags to mark the start and end of our script code.
The tag we use to do this is the <script> tag.
Basically when the browser spots <script> tags, instead of trying to display the contained text to the user, it uses the browser's built-in JavaScript interpreter to run the code's instructions.
We can put the <script> tags inside the header (between the <head> and </head> tags), or inside the body (between the <body> and </body> tags) of the HTML page.
The <script> tag has a number of attributes, but the most important one for us are the language and type attributes.
So, our opening script tag will look like this: <script language="JavaScript" type="text/javascript">

try out a simple example of using JavaScript to change the background color of the browser.
<html> <body BGCOLOR="WHITE"> <p>Paragraph 1</p> <script language="JavaScript" type="text/javascript"> document.bgColor = "RED"; </script> </body> </html>
Save and load the page in your browser
Link to file

we use JavaScript to set the document's background color to red.
document.bgColor = "RED";
You'll also see that there's a semicolon (;) at the end of the line. We use a semicolon in JavaScript to indicate the end of a statement.
to tell the browser to stop interpreting our text as JavaScript and start interpreting it as HTML, we use the script close tag:
</script>

<html> <body BGCOLOR="WHITE"> <p>Paragraph 1</p> <script language="JavaScript" type="text/javascript"> // Script block 1 alert("First Script Block"); </script> <p>Paragraph 2</p> <script language="JavaScript" type="text/javascript"> // Script block 2 document.bgColor = "RED"; alert("Second Script Block"); </script> <p>Paragraph 3</p> </body> </html>
Save and load the page in your browser

The first line
// Script block 1
is just a comment, solely for our benefit. The browser recognizes anything on a line after a double forward slash (//) to be a comment and does not do anything with it.
The alert() function in the second line of code is also new to us.
A function takes some information, processes it, and gives you a result.
the alert() function enables us to alert or inform the user about something, by displaying a message box.