Technologies

 


JavaScript Operators

Arithmetic Operators

Operator

Description

Example

Result

+

Addition

x=2
y=2
x+y

4

-

Subtraction

x=5
y=2
x-y

3

*

Multiplication

x=5
y=4
x*y

20

/

Division

15/5
5/2

3
2.5

%

Modulus (division remainder)

5%2
10%8
10%2

1
2
0

++

Increment

x=5
x++

x=6

--

Decrement

x=5
x--

x=4

Assignment Operators

Operator

Example

Is The Same As

=

x=y

x=y

+=

x+=y

x=x+y

-=

x-=y

x=x-y

*=

x*=y

x=x*y

/=

x/=y

x=x/y

%=

x%=y

x=x%y

Comparison Operators

Operator

Description

Example

==

is equal to

5==8 returns false

===

is equal to (checks for both value and type)

x=5
y="5"
x==y returns true
x===y returns false

!=

is not equal

5!=8 returns true

> 

is greater than

5>8 returns false

< 

is less than

5<8 returns true

>=

is greater than or equal to

5>=8 returns false

<=

is less than or equal to

5<=8 returns true

Logical Operators


Operator

Description

Example

&&

and

x=6
y=3
(x < 10 && y > 1) returns true

||

or

x=6
y=3
(x==5 || y==5) returns false

!

not

x=6
y=3
!(x==y) returns true

String Operator

A string is most often text, for example "Hello World!". To stick two or more string variables together, use the + operator.


txt1="What a very"
txt2="nice day!"
txt3=txt1+txt2 

The variable txt3 now contains "What a verynice day!".
To add a space between two string variables, insert a space into the expression, OR in one of the strings.


txt1="What a very"
txt2="nice day!"
txt3=txt1+" "+txt2
or
txt1="What a very "
txt2="nice day!"
txt3=txt1+txt2

The variable txt3 now contains "What a very nice day!".

Conditional Operator

JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.

Syntax

variablename=(condition)?value1:value2 

Example

greeting=(visitor=="PRES")?"Dear President ":"Dear "

If the variable visitor is equal to PRES, then put the string "Dear President " in the variable named greeting. If the variable visitor is not equal to PRES, then put the string "Dear " into the variable named greeting.

JavaScript Popup Boxes

In JavaScript we can create three kind of popup boxes: Alert box, Confirm box, and Prompt box.

Examples

Alert box
Alert box with line breaks
Confirm box
Prompt box

Alert Box

An alert box is often used if you want to make sure information comes through to the user.
When an alert box pops up, the user will have to click "OK" to proceed.
Syntax:


alert("sometext")

Confirm Box

A confirm box is often used if you want the user to verify or accept something.
When a confirm box pops up, the user will have to click either "OK" or "Cancel" to proceed.
If the user clicks "OK", the box returns true. If the user clicks "Cancel", the box returns false.
Syntax:


confirm("sometext")

Prompt Box

A prompt box is often used if you want the user to input a value before entering a page.
When a prompt box pops up, the user will have to click either "OK" or "Cancel" to proceed after entering an input value.
If the user clicks "OK" the box returns the input value. If the user clicks "Cancel" the box returns null.
Syntax:


prompt("sometext","defaultvalue")

JavaScript Functions

A function is a reusable code-block that will be executed by an event, or when the function is called.

Examples

Function
How to call a function.
Function with arguments
How to pass a variable to a function, and use the variable in the function.
Function with arguments 2
How to pass variables to a function, and use these variables in the function.
Function that returns a value
How to let the function return a value.
A function with arguments, that returns a value
How to let the function find the product of 2 arguments and return the result.

JavaScript Functions

To keep the browser from executing a script as soon as the page is loaded, you can write your script as a function.
A function contains some code that will be executed only by an event or by a call to that function.
You may call a function from anywhere within the page (or even from other pages if the function is embedded in an external .js file).
Functions are defined at the beginning of a page, in the <head> section.

Example

<html>
<head>
<script type="text/javascript">
function displaymessage()
{
alert("Hello World!")
}
</script>
</head>
<body>
<form>
<input type="button" value="Click me!"
onclick="displaymessage()" >
</form>
</body>
</html>


If the line: alert("Hello world!!"), in the example above had not been written within a function, it would have been executed as soon as the line was loaded. Now, the script is not executed before the user hits the button. We have added an onClick event to the button that will execute the function displaymessage() when the button is clicked.
You will learn more about JavaScript events in the JS Events chapter.

How to Define a Function

The syntax for creating a function is:


function functionname(var1,var2,...,varX)
{
some code
}

var1, var2, etc are variables or values passed into the function. The { and the } defines the start and end of the function.
Note: A function with no parameters must include the parentheses () after the function name:


function functionname()
{
some code
}

Note: Do not forget about the importance of capitals in JavaScript! The word function must be written in lowercase letters, otherwise a JavaScript error occurs! Also note that you must call a function with the exact same capitals as in the function name.

The return Statement

The return statement is used to specify the value that is returned from the function.
So, functions that are going to return a value must use the return statement.

Example

The function below should return the product of two numbers (a and b):


function prod(a,b)
{
x=a*b
return x
}

When you call the function above, you must pass along two parameters:


product=prod(2,3)

The returned value from the prod() function is 6, and it will be stored in the variable called product.
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