Desicion Making

Very often while writing code, there is a need for performing different actions for different decisions. Conditional statements are used to meet those needs. Javascript offers the following conditional statements
if condition to decide to execute a block of code when the specified condition is true.
else condition to decide to execute a block of code when the condition specified in if is false.
else if  to specify a new condition to execute a new block when the first condition is false
switch to jump between many alternative blocks of code based on the requirement
 

The if Statement

if condition to decide to execute a block of code when the specified condition is true.

Syntax:

if (condition) {
    block of code to be executed if the condition is true
}

Example

<!DOCTYPE html>
<html>
<body>
<p id="demo">a is greater than b</p>
<script>
var a=10;
var b=20;
if (a<b) {
    document.getElementById("demo").innerHTML = "a is less than b";
}
</script>
</body>
</html>


Output

a is less than b
 

Try

The if else statement:

The 'if...else' statement is the next form of control statement that allows JavaScript to execute statements in a more controlled way.

Syntax:

if (expression){
   Statement(s) to be executed if expression is true
}
else{
   Statement(s) to be executed if expression is false
}

Example:

<html>
<body>
<script>
var a=10;
var b=20;
if (a>b) {
    document.write("a is less than b");
}
else{
        document.write("a is greater than b");
}
</script>
</body>
</html>
 

Output:
a is greater than b 

Try

The else if Statement

else if statement is used to specify a new condition which will be assesed when the first condition is false.

Syntax:

if (condition1) {
    block of code to be executed if condition1 is true
} else if (condition2) {
    block of code to be executed if the condition1 is false and condition2 is true
} else {
    block of code to be executed if the condition1 is false and condition2 is false
}

Example:

<!DOCTYPE html>
<html>
<body>
<script>
    var greeting;
    var time = new Date().getHours();
    if (time < 10) {
        greeting = "Good morning";
    } else if (time < 20) {
        greeting = "Good day";
    } else {
        greeting = "Good evening";
    }
document.write(greeting);
</script>
</body>
</html>


Output:

Good day
 

The Switch Statement

switch statement is used to select one of many blocks of code to be executed.

Syntax:

switch(expression) {
    case n:
        code block
        break;
    case n:
        code block
        break;
    default:
        code block
}
This is how it works:

The switch expression is evaluated once.
The value of the expression is compared with the values of each case.
If there is a match, the associated block of code is executed.

Example:

<!DOCTYPE html>
<html>
<body>
 
<script>
var i=2;
switch(i){
        case 0:
       document.write("i equals to 0");
       break;
    case 1:
       document.write("i equals to 1");
       break;
    case 2:
       document.write("i equals to 2");
       break;
    default:
        document.write("i equals to 0 or 1 or 2");
}
</script>
</body>
</html>


Output:

i equals to 2