JS-Slides-2_74526582652945_73562876535.ppt

2. JavaScript DataTypes
JavaScript allows you to work with three primitive data types:
• Numbers eg. 123, 120.50 etc.
• Strings of text e.g. "This text string" etc.
• Boolean e.g. true or false.
JavaScript also defines two trivial data types, null and undefined,
each of which defines only a single value.
In addition to these primitive data types, JavaScript supports a
composite data type known as object. We will see an object
detail in a separate chapter.

JavaScript Variables:
 Like many other programming languages, JavaScript has
variables. Variables can be thought of as named containers. You
can place data into these containers and then refer to the data
simply by naming the container.
• Before you use a variable in a JavaScript program, you must
declare it. Variables are declared with the var keyword as follows:
<script type="text/javascript">
<!–
var money;
var name;
//-->
</script>

You can also declare multiple variables with the same var keyword
as follows:
<!–
var money, name;
//-->
</script>
Note: Use the var keyword only for declaration or
initialization.once for the life of any variable name in a
document. You should not re-declare same variable twice.
Client-side JavaScript:

JavaScript Variable Scope
• The scope of a variable is the region of your program in which it
is defined. JavaScript variable will have only two scopes.
– Global Variables: A global variable has global scope which means it is
defined everywhere in your JavaScript code.
– Local Variables: A local variable will be visible only within a function where it
is defined. Function parameters are always local to that function.
<!–
var myVar = "global"; // Declare a global variable
function checkscope( )
{ var myVar = "local"; // Declare a local variable
document.write(myVar);
}
//-->
</script>

JavaScript Variable Names:
• You should not use any of the JavaScript reserved keyword as
variable name. These keywords are mentioned in the next
section. For example, break or boolean variable names are not
valid.
• JavaScript variable names should not start with a numeral (0-9).
They must begin with a letter or the underscore character. For
example, 123test is an invalid variable name but _123test is a valid
one.
• JavaScript variable names are case sensitive. For example, Name
and name are two different variables.

3. JavaScript Operators
 Arithmetic Operators
 Comparision Operators
 Logical (or Relational) Operators
 Assignment Operators
 Conditional (or ternary) Operators

Assume variable A holds 10 and variable B holds 20 then:
The Arithmatic Operators:

The Assignment Operators:
• Note: Same logic applies to Bitwise operators so they will become like <<=, >>=,
>>=, &=, |= and ^=.

Miscellaneous Operator
The Conditional Operator (? :)
The typeof Operator
• The typeof is a unary operator that is placed before its single
operand, which can be of any type. Its value is a string indicating
the data type of the operand.
• The typeof operator evaluates to "number", "string", or "boolean"
if its operand is a number, string, or boolean value and returns
true or false based on the evaluation.

4. Conditional statements:
In JavaScript we have the following conditional statements:
• if statement - use this statement to execute some code only if
a specified condition is true
• if...else statement - use this statement to execute some code if
the condition is true and another code if the condition is false
• if...else if....else statement - use this statement to select one
of many blocks of code to be executed
switch statement - use this statement to select one of many
blocks of code to be executed

Example 1:
<!DOCTYPE html>
<html>
<body>
<p>Click the button to get a time-based greeting.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>function myFunction()
{
var x="";
var time=new Date().getHours();
if (time<10) { x="Good morning"; }
else if (time<20) { x="Good day"; }
else { x="Good evening"; }
document.getElementById("demo").innerHTML=x;
}
</script>
</body>
</html>

Example 2: switch statement
Demonstrate with FreeJavaScript Editor

JS-Slides-2_74526582652945_73562876535.ppt

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