Javascript Basics: continued

The purpose of this page is to demonstrate some of the features of HTML that you should be using in your work.

Values: For javascript scripts to work, there must be some content so that the browser knows what to when an event handler has been triggered

Values provide this content and come in several different forms

They can contain numbers or words and are used in several different ways

Examples of values include:

Other properties of documents include:

value type		Meaning		Example
Numerical		Any number		247365
String		Any characters inside " "		"Like this!"
Boolean operator		True/False		True
These are also values but less frequently used
Null		Empty, no meaning
Object		value linked to an object
Function		value returned by a function

Variable:When you use a variable in a script, you assign it to a variable

For example, a string value could be the title of a web page, such as "Javascript Tutorial"

To use this value, you have to assign it to a variable, such as "myPage"

It would look like this:

myPage = "Javascript Tutorial"

In this syntax, the < = > is shorthand for "is set to", so the statement actually reads:

The variable "mypage" is set to the value "Javascript Tutorial"

You can create as many variables as you need

Variable names follow UNIX conventions: no spaces or punctuation

They are also case sensitive:

"myPage" is not the same variable as "MyPage"

Operators: to use variables in a script, they must be linked together with operators

These are taken from math and have similar meanings

Here are some common operators:

Operator name		Meaning		Example
x + y (numeric)		Adds x and y		3 + 5 = 8
x + y (string)		Adds text of x and y		Dog + head = Doghead
x - y		Subtracts y from x		5 - 3 = 2
x * y		Multiplies x and y		3 * 5 = 15
x / y (string)		Divides x by y		15 / 3 = 5
x % y		Remainder when x is divided by y (Modulus)		15 % 4 = 3
x + +		Adds 1 to x (after operation is over)		y = x + + (if x = 9: y = 9, x = 10)
+ + x		Adds 1 to x (before operation is over)		y = x + + (if x = 9: y = 10, x = 10)
x - -		Subtracts 1 from x (after operation is over)		y = x - - (if x = 9: y = 9, x = 8)
- - x		Subtracts 1 from x (before operation is over)		y = x - - (if x = 9: y = 8, x = 8)
- x		Reverses sign on x		- x (if x = 4, - x = - 4

Comparisons: To compare variables in a script, or to compare a script variable against the input provided by a user, comparisons are used

Here are the major comparisons you can use:

Comparison name		action
x==y		If x equals y, it returns true		3 + 5 = 8
x!=y		If x does not equals y, it returns true		Dog + head = Doghead
x>y		If x is greater than y, it returns true		5 - 3 = 2
x>=y		If x is greater than or equal to y, it returns true		3 * 5 = 15
x<y		If x is less than y, it returns true		15 / 3 = 5
x<=y		If x is less than or equal to y, it returns true		15 % 4 = 3
x&&y		If x and y are both true, it returns true		y = x + + (if x = 9: y = 9, x = 10)
x||y		If either x or y is both true, it returns true		y = x + + (if x = 9: y = 10, x = 10)
!x		If x is false, it returns true		y = x - - (if x = 9: y = 9, x = 8)

Here's how to begin putting scripts together