A conditional statement is
a set of instructions that executes depending upon the condition is
true or false.
As per MDN, JavaScript
supports two conditional statements if…else and switch case.
JavaScript is a computer
language mainly used for making Interactive websites under Web
development.
if
statement:
Statements inside if will
be executed if the expression is true. If the expression is false
then no statements will be executed. We will be using comparison
operators to evaluate the expression.
Syntax:
if (expression)
{
statements will be
executed only if the expression is true
}
Example:
<html>
<body>
<script
type="text/javascript">
var age =
prompt('Enter your age plz');
if( age
>=18 ){
alert("Qualifies for driving");
}
</script>
</body>
</html>
Result:
Enter your age
plz: 25
Qualifies for
driving.
If we enter age
greater than 18 then it will execute the statement otherwise will
come out.
if ….else
statement
It is the next
form of control statements which allows to execute statements
depending upon the expression is true or false.
Syntax:
if
(expression)
{
statements
will be executed only if the expression is true
}
else {
statements
will be executed only if the expression is false
}
Example:
<html>
<body>
<script
type="text/javascript">
var age =
prompt('Enter ur age plz');
if( age
>=18 ){
alert("Qualifies for driving");
}
else{
alert(“Doesn’t qualify for driving”);
}
</script>
</body>
</html>
Result:
Enter your age
plz: 25
Qualifies for
driving
Enter your age
plz: 15
Doesn’t
qualify for driving
If age is
greater than or equal to 18 then it will execute the if statement
otherwise will execute the else statement.
if else if
statement:
This is more
advanced form of if..else that will execute statements on the basis
of given conditions. It is useful in the case of multiple
conditions. In this case only the first logical condition which is
true will be executed.This can also be known as nested if statements.
Syntax:
if
(expression1){
statements
will be executed only if the expression2 is true
}
else if
(expression2){
statements
will be executed only if the expression2 is true
}
else if
(expression3){
statements
will be executed only if the expression3 is true
}
else {
statements
will be executed only if the expression is false
}
Example:
<html>
<body>
<script
type="text/javascript">
var book
= prompt('Enter bookname');
if( book
= ‘Kiterunner’ ){
alert("It
comes under fiction category");
}
else if(
book = ‘Wasted in Engineering’ ){
alert("It
comes under non fiction category");
}
else if(
book = ‘A history of India’ ){
alert("It
comes under history category");
}
else{
alert(‘Unknown category’);
}
</script>
</body>
</html>
Result:
It will display
the result on the basis of the choices given. If we will enter
Kiterunner in the prompt box, then ‘It
comes under fiction category’ will be the output. If we will enter
any bookname which is not mentioned, example ‘Madhushala’, then
result will be ‘unknown category’. For comparison use == (equal
operator). For comparison don’t use =. ‘=’ is used for
assigning values not for comparing them.
SWITCH
CASE
The main objective of
switch case is to execute different statements given on the basis of
expression given. Each case statement will be checked against the
expression given until a match is found. If nothing founds default
statement will be executed. Break is very important after each
statement. If we will not give it then every statement will be
executed.
Syntax:
switch
(expression)
{
case
condition 1: statement(s)
break;
case
condition 2: statement(s)
break;
case
condition n: statement(s)
break;
default:
statement(s)
}
Example:
<!DOCTYPE html>
<html>
<head>
<title>Switch
Case</title>
</head>
<body>
<script type="text/javascript">
<script type="text/javascript">
var time = new Date();
var myday =
time.getDay();
//alert(myday);
switch(myday){
case 0:
alert('it is sunday');
break;
case 1:
alert('it is monday')
break;
case 2:
alert('it is tuesday')
break;
case 3:
alert('it is wednesday')
break;
case 4:
alert('it is thursday')
break;
case 5:
alert('it is friday')
break;
case 6:
alert('it is saturday')
break;
default:break;
}
</script>
</body>
</html>
In the above example, new
Date() function will display the current date and date with time
zone.
In the above example, new
Date() function will display the current date and date with time
zone. The getDay() function in JavaScript returns the weekday as a number between 0
and 6. (Sunday=0, Monday=1, Tuesday=2, Wednesday =3, Thursday=4,
Friday=5, Saturday=6). Result will be current day and it will execute
the case depending upon on which day it has been executed. For
example. If we are executing it today, i.e. 21st April 2016. It will
find the match with Case 4 and execute it. Result will be “it is
Thursday”.
