1. The <script> Tags

The <script> tags appear at the beginning and end of every individual Javascript. The ending can only be written as </script>, and every Javascript MUST be closed. Otherwise, there will be errors on the page, and extra parts of the page that weren't part of the script might also be missing. It's messy. So please close your scripts. The beginning can be written as plain <script>, but you can also specify by adding things like this: <script language="javascript">. Or if you really want to be specific, with versions for example, write something like this: <script language="javascript 1.2">. If you truly want to be specific down to very last character, use this: <script language="javascript1.2" type="text/javascript">. As far as I know, it really does not matter whether you specify a language or version of a language in your scripts. They still seem to work unspecified in my testing. Still, I have also heard that it's much safer to specify a language, for there are multiple languages out there, and you would not want to risk having an error on your pages, would you?

The beginning script tag can also link to a .js file (a Javascript file). In such a case, a webmaster would place the script code inside a separate .js file instead of in the HTML file. Whenever the script is external, a webmaster links to it using the beginning script like this:

<script language="javascript" src="example.js" type="text/javascript">

Not all browsers are capable of reading all the kinds of Javascript (or a mixture of both). To prevent error messages from popping up left and right on the visitor's screen, webmasters use the concept of the comment to hide the script from only the older browsers and not the new ones. Using the <!-- and --> of the comment code, double slashes // are used to only hide the script from the browsers that cannot read the script. The double slashes // are Javascript comments. An example of this hiding code looks like this:

<script>
<!--

(And the script contents will go here.)

//-->
</script>

As I mentioned above, the double slash // is the code of the Javascript comment. A comment is basically any text that you want hidden from the page. It's usually used by webmasters to label things or write instructions next to parts of the code for organization and the prevention of confusion when working with very long scripts. You can put whatever you want in the comments, and it won't show. Javascript comments can be placed anywhere within the opening and closing script tags. Comments look like this:

<script>
//This is a comment. I can write whatever I want here, and it won't show. !@#$%^&*()
//Wheeeeeeeeeeeee!!!!!!!!!!! Comments...fun!

(And the script contents will go here, and comments can be placed within the script contents itself, as long as the contents are modified themselves.)
//Monkey comment in the middle!
(In other words, the contents can be split by comments and still work.)


//Comments galore! Comments make the world go 'round! :)
</script>

I cannot write my own Javascript scripts yet, but knowing what the common commands more or less mean helps one's understanding of Javascript. Here are few commands I more or less know so far.

onMouseOver - This is used for functions related to the moving of the cursor (mouse arrow) over something, be it a link, text, image, button, or whatnot.
onMouseOut - This is usually used after onMouseOver and is used when a cursor is moved away from a hovering position over a link, text, image, button, or whatnot.

window - This is not necessarily used alone. It's normally used with something added to it, as shown in the two examples below. This is used with functions involving the window of the browser, like in the launching of a new window or the maximizing of the current one.
      window.alert

document - This is used for the creation or modification of contents or aspects of a webpage or HTML document, hence the name of the 'document' in the command. For example, it could be used to create text on the webpage or tamper with the colors on the page. Below are some examples of the document part of the script.
      document.write
      document.bgcolor

*Disclaimer: This was my second incomplete attempt at a concise overview of Javascript. It assumes that you already know HTML cold, and that you either a) already know C, C++, Java, etc., or b) can figure out what everything means from the code alone. And I won't explain the terms yet. I probably will when I have more time.

Script and Using Comments to Hide Script From Older Browsers

<script language="Javascript">
<!--

//-->
</script>


<script>
<!--

//-->
</script>


<script>

</script>

Terms to Know: attributes
Variables and Write

var blah
blah = 3.14

var blahblah = 42
blahblah = "I am a jelly donut."
document.write(blahblah)

document.write("I am the master.<br>Do you like cheese?")

document.write("<img src='image.gif'>")
document.write('<img src="image.gif">')

Terms to Know: local variables, global variables, declaring variables, initializing variables, string
Operators

x+y  (numeric addition or string concatenation)
x-y
x*y
x/y
x%y  (remainder of x/y, modulus or mod.)
x++  (x=x+1)
++x  (x=x+1)
x--  (x=x-1)
--x  (x=x-1)
-x   (reverse sign of x)

var x = 3
var y = 4

x+y

var a = "I like "
var b = "cheese."

a+b

Terms to Know: operator, operand, concatenation, modulus
if, else, functions...

if (x==y)
	{
   	document.write("x equals y")
   	}
else
	{
   	document.write("x does not y")
	}

x == y   x and y are equal 
x != y   x and y are not equal 
x > y    x is greater than y 
x >= y   x is greater or equal to y 
x < y    x is less than y 
x <= y   x is less than or equal to y 

if (age < 20 && age >= 12){
  document.write('You are a teen.')
  }

Terms to Know: condition, statement
Functions

function myAdder (number1, number2)
	{
	var total = number1 + number2
	return total
	}
document.write(myAdder(23, 56))


var today = new Date()
document.write(today)

Terms to Know: function
Events

Click <a href='JavaScript:alert("Attention, your speaking rights have been suspended")'>here</a>.

Click <a href='JavaScript:alert(myFunction)'>here</a>.

<form name="clickbuttongetsanalert">
<input type="button" name="alert" value="Click for Alert"
onClick='alert("Yahoo!")'>
</form>

<form name="clickbuttongetsconfirmation">
<input type="button" name="confirmDemo" 
value="Confirm dialog box"
onClick='confirm("Can you think of a use for this?")'>
</form>

<form name="clickbuttongetspromptdialog">
<input type="button" name="promptDemo" 
value="Prompt dialog box"
onClick='prompt("Enter some information")'>
</form>