JavaScript Tutorial: JavaScript Statements
In JavaScript we use statements that tell the script
to check to see if something is true - or present - or not. Common JavaScript
statements are if, for, else, and else if. These statements are very important
to JavaScript, and you will be using them a lot when you write your own
JavaScript.
Let's first look at the 'if' statement. We use if to check for equalities.
The if statement always includes the parentheses () after it, and what we
are checking for goes inside the parentheses. We also use curly brackets
{}with the if statement. The code that we want to run is inside the curly
brackets.
So, what the script does is it looks to see if the condition that we have
specified in the parentheses exists, and if it does, it runs the code inside
the curly brackets that follow it. If the condition does not exist, it skips
the code inside the curly brackets. Here is an example:
var a = 1;
var b = 2;
var c = 3;
if ((a != 0) || ( (b >= 2) && !(c > 9) ))
{
document.write("This is right.");
} |
Now, you see on the if statement that we've used some
characters: !, | |, &&, and >. These characters all mean
something.
The ! character stands for NOT. In our example, it means if a is not equal
to 0.
The | | characters means OR and the > character means greater than. Our
example now reads if a is not equal to 0 or b is not greater than 2.
The && Characters mean AND. The statement now reads if a is not equal
to 0 or b is greater than 2 and it is not true that c is greater than 9.
Now, if this statement is true, or the condition exists, the code inside
the curly brackets will run, and the words This is right will be printed
on the web page. Using the ! character before a statement changes the meaning
of the statement to mean that it is NOT true. In this example, c is greater
than 9 is NOT true.
Pay special attention to how parentheses are used in the example. This is
very important, and if it isn't done correctly, the script will not run.
Next is the else statement. Else would be used if the if statement is not
true. If you will have more than two possible conditions, you would use if
first, followed by else if, followed by else. You can have as many else if
statements as you need.
var a = 0;
if (a > 0)
{ do something };
else if { do something else };
else { do this }; |
The JavaScript reads from top to bottom. If the if statement
is true, it runs the code in the curly brackets, and ignores the else if
and else statement that follows.
The for statement is used to perform a loop. This means
that the script will run the same piece of code for however many times you
specify. Here is an example:
for (var a=0; a<10; a++)
{ document.write("Test" + a); } |
This statement says that as long as a is less than 10,
the code inside the curly brackets should run. Furthermore, each time the
code is run, it should be increased by 1. This is indicated with the double
plus signs. You could also have it decrease by 1 each time by using a double
minus sign, - -
|
|
Previous |
Next |
JavaScript Tutorial: An Introduction
to JavaScript
The Basics of
JavaScript
JavaScript
Events
JavaScript
Variables and Arrays
JavaScript
Statements
JavaScript
Functions and Methods
JavaScript
Errors
JavaScript Food
Chain
Writing JavaScript
Code
JavaScript
Object Reference
JavaScript
Events Reference
JavaScript
Functions Reference
JavaScript
Math Object Reference
JavaScript Array Object
Reference
JavaScript String Object
Reference
JavaScript
Date Object Reference
Web Development Tutorials
Cascading Style
Sheets Tutorial: An Introduction to Cascading Style Sheets
JavaScript
Tutorial: An Introduction to JavaScript
Web
Development: A step by step guide to developing a successful Internet
business
HTML
Codes Chart: Copy and paste HTML codes for your web page
HTML Tips:
Copy and paste special effect HTML codes for your web page
Web Design
Tips: Tips, tricks, and special effect codes for your web page
JavaScript
Code Snippets: Copy and paste special effect JavaScript codes for your
web page
216
Web Safe Color Chart: Hexadecimal and RGB Color Codes for your web page
ASCII Character
Codes Chart: American Standard Code for Information
Interchange character codes chart
|
|