Everything
in our day to day life is impacted by conditions. Similarly in Java
Script too conditions play a vital role in code execution and its
structure. Every JS function must be designed as per the condition of
the work we are looking to be done by it. There are many conditions
in which the code can be written and simultaneously a code can also
be written in many ways following a similar condition. We will see
few e.g. below to understand this in a better way but before that
lets understand few conditional statements.
If, else, else-if and switch statements in JavaScript :
The word if
and else itself states it clearly that certain things to be done only
if following rule is fulfilled Or else don’t do it or do
something else.
Suppose if
you want to do something only in any particular condition then you
use the if statement. These are used for much complicated
functions with multiple conditions as are easy to understand and
maintain that switch.
Example:
If
we want an alert “Yay its Banana” only if the fruit selected is
Apple.
<script
type="text/javascript">
var fruit
= "Banana";
if(fruit
== 'Banana'){
alert('Yay
Its Banana'); //Yay Its Banana
}
</script>
If-else statement
Similarly as
above eg. there was just one condition but now if we want more than a
condition like alert “Its still Banana” only if Banana is the
fruit selected or alert “Are you sure?”
<script
type="text/javascript">
var fruit
= "Orange";
if(fruit
== 'Banana')
{
alert('Its
still Banana);
}
else
{
alert("Are
you sure ?"); //Are you sure ?
(This is because 1st
condition is not fulfilled hence second the else one initiated.)
}
</script>
else-if statement
Similarly if
you want multiple conditions you can use it as many times as you need
as per the conditions but if one condition use if, If two conditions
use if and else but if more that two conditions use else if further
till last one like in e.g. below.
<script
type="text/javascript">
var
fruit = "Mango";
if(fruit
== 'Banana'){
alert('Yay
Its Banana');
}
else
if(fruit == 'Appie')
{
alert("Have
you selected Apple ?");
}
else
if(fruit == 'Mango'){
alert("Have
you selected Mango ?"); //Have you
selected Mango ? (As 3rd
condition fulfilled.)
}
else
{
alert(“Please
choose any fruit.”);
}
</script>
Nested
Conditions:
Nesting means a condition
under a condition. Like in the below eg. under first if condition you
have 1 more if condition that if color is red and color2 is green
change bg color to yellow. Or if color 1 still remains red change bg
to red.
Eg.
<!DOCTYPE
html>
<html>
<head>
<title>JavaScript
Basics</title>
<style
type="text/css">
.bgRed{background-color:
red}
.bgGreen{background-color:
green}
</style>
</head>
<body>
<button
id="btn">Change Color</button>
<script
type="text/javascript">
function
colorChanger(){
var
getColor = prompt('Enter a color');
var
getColor2 = prompt('Enter a color');
if(getColor=='red'){
if(getColor2=='green'){
document.body.style.backgroundColor
= 'yellow';
}else{
document.body.style.backgroundColor
= 'red';
}
}else
if(getColor=='blue' && getColor2=='green'){
document.body.style.backgroundColor
= 'cyan';
}else
if(getColor=='red' && getColor2=='blue'){
document.body.style.backgroundColor
= 'magenta';
}else{
document.body.style.backgroundColor
= 'white';
}
}
document.getElementById('btn').onclick
= colorChanger;
</script>
</body>
</html>
Like
if else condition is used for multiple conditions similarly switch is
also used for multiple conditions. But in a switch we cannot
use assignment operators to define less than or greater than values, we have to give exact values
for it and no dynamic values can be given in it.
Example:
<!DOCTYPE html>
<html>
<head>
<title>JavaScript
Basics</title>
<style
type="text/css">
.bgRed{background-color:
red}
.bgGreen{background-color:
green}
</style>
</head>
<body>
<button
id="btn">Change Color</button>
<script
type="text/javascript">
function colorChanger(){
var getColor =
prompt('Enter a color');
switch(getColor){
case 'red':
document.body.className
= 'bgRed';
break;
case 'green':
document.body.className
= 'bgGreen'; //Here no assignment
operators are used just
values are assigned in case as green, red etc …
break;
default:
alert('Enter red or
green color');
break;
}
}
document.getElementById('btn').onclick
= colorChanger;
</script>
</body>
</html>
Why Boolean LogicalOperator are important to work with conditions in JavaScript?
- && (And)
- || (Or)
- ! (Not Equal to)
If suppose we have a case
where we want a code to be run specifically if we get both of the 2
conditions fulfilled.
Example: I want an alert
that “Its correct” only if both of these conditions are fulfilled
where in fruit selected is Apple and taste selected is Sweet.
<script
type="text/javascript">
var fruit = "Apple";
var taste = "Sweet";
if((fruit == 'Apple') &&
(taste == 'Sweet')){ //Thats correct
Both conditions are must to be fulfilled.
alert("Thats
correct");
}
</script>
Eg. Similarly if we want
any one condition to be fulfilled where in fruits Apple is selected
Or if taste Sweet is selected.
<script
type="text/javascript">
var fruit = "Mango";
var taste = "Sweet";
if((fruit == 'Apple') ||
(taste == 'Sweet')){ //One condition is
fulfilled
alert("One
condition is fulfilled");
}
</script>
Eg. If we want that the
selected variable should not have a particular value ie negation
condition, we can do it with not equal condition Operator.
<script
type="text/javascript">
var game = "Cricket";
if((fruit !=
'Cricket'){ //Yes its not !
alert("Yes its not
!");
}
</script>
What are Conditional
Operator or Ternary Operator?
It is a short condition to
be used in some places. The syntax of conditional operator is:
var result = (condition) ?
true expression : false expression;
Example:
var age = 45;
var result = (age ==
45)?'You are 45yrs old.':'You are not 45yrs old.';
alert(result); //You are
45yrs old.
Summary:
We can use various
available conditionals in JavaScript according to the situation. At
first glance all the conditions look like an alternative of each
other but seriously speaking this is not the case always. As much you
will indulge in them more sense you will acquire to use them.
