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JavaScript Primer

An HTML file can contain text, HTML tags and scripts. Scripts in an HTML file can be executed by the browser.

What is JavaScript?

JavaScript is used in millions of Web pages to improve the design, validate forms, detect browsers, create cookies, and much more.

JavaScript is the most popular scripting language on the internet, and works in all major browsers.

JavaScript is about "programming" the behavior of the browser. This is called client-side scripting or browser scripting.

Server-side scripting is about "programming" the behavior of the server (see Web Scripting chapter).

JavaScript gives HTML designers a programming tool - HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages
JavaScript can put dynamic text into an HTML page - A JavaScript statement like this: document.write("<h1>" + name + "</h1>") can write a variable text into an HTML page
JavaScript can react to events - A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element
JavaScript can read and write HTML elements - A JavaScript can read and change the content of an HTML element
JavaScript can be used to validate data - A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing
JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser
JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer

<html>
<body>
<script type="text/javascript">
document.write("Hello World!")
</script>
</body>
</html>

The code above will produce this output on an HTML page:

Hello World!

To insert a JavaScript into an HTML page, we use the <script> tag. The type attribute defines the scripting language.

So, the <script type="text/javascript"> tells where the JavaScript starts:

<script type="text/javascript">

The JavaScript command for writing some output to a page is document.write:

document.write("Hello World!")

Then, the script ends:

</script>

Write text
How to write text on a page.

Write text with formatting
How to format the text on your page with HTML tags.