Conditional Statements

A conditional statement is a programming construct that allows you to execute different blocks of code based on whether a certain condition is true or false.

1. if

Syntax

if(condition)
{
   //statement
}

Code

<!DOCTYPE html>
<html>
 <head>
   <title>Hello JS 💛</title>
   <script>
     const age = 20;

      if(age>18)
      {
        document.write("You are eligible for voting...")
      }
   </script>
 </head>
 <body></body>
</html>

Output

You are eligible for voting...

In the above program value 20 to the variable age, and then checks if age is greater than 18 using an if statement. If the condition is true, the code inside the block is executed, which in this case is a call to the document.write() function to display the message "You are eligible for voting..." on the web page.

2. if-else

Syntax

if(condition)
{
   //statement
}
else
{
   //statement
}

Code

<!DOCTYPE html>
<html>
 <head>
   <title>Hello JS 💛</title>
   <script>
     const age = 16;

      if(age>18)
      {
        document.write("You are eligible for voting...")
      }
      else
      {
        document.write("You are not eligible for voting...")
      }
   </script>
 </head>
 <body></body>
</html>

Output

You are not eligible for voting...

In this program, the age is assigned to a constant variable age with the value of 16. The if statement checks if the age is greater than 18. If the condition is true, it will execute the document.write() statement with the message You are eligible for voting.... If the condition is false, it will execute the else block with the message You are not eligible for voting....

Since the age value in this case is 16, which is less than 18, the output of the program would be You are not eligible for voting...

Program : Use if-else and write JS program to check if given number is positive or negative.

Code

<!DOCTYPE html>
<html>
  <head>
    <title>Hello JS 💛</title>
    <script>
     const num = parseInt(prompt("Enter any Number: "));

     if(num<0)
     {
        document.write("Negative Number");
     }
     else
     {
        document.write("Positive Number")
     }
    </script>
  </head>
  <body></body>
</html>

2. if-else-ladder

Syntax

if(condition A)
{
   //statement
}
else if (condition B)
{
   //statement
}
else if (condition C)
{
   //statement
}
else
{
 //statement
}

Code

<!DOCTYPE html>
<html>
 <head>
   <title>Hello JS 💛</title>
   <script>
     const num = 1;

      if(num==1)
      {
        document.write("One")
      }
      else if(num==2)
      {
        document.write("Two")
      }
   else if(num==3)
   {
   document.write("Three")
   }
   else
   {
     document.write("Not Match")
   }
   </script>
 </head>
 <body></body>
</html>

Output

One

This code will output One because the value of the variable num is 1 and the first if statement checks if num is equal to 1. Since this condition is true, the code inside the first if statement will execute, which is to write One to the document.

If the value of num were 2, the second else if statement would execute and the code would write Two to the document. Similarly, if num were 3, the third else if statement would execute and the code would write Three to the document. If the value of num were anything other than 1, 2, or 3, the else statement would execute and the code would write Wrong input to the document.

nested-if

A nested if statement is a conditional statement that is nested within another conditional statement. This is useful when you need to test multiple conditions in order to execute a block of code.

Code

<!DOCTYPE html>
<html>
 <head>
   <title>Hello JS 💛</title>
   <script>
   const jeeMain = 130;
   const jeeAdv = 120;

   if(jeeMain>120 && jeeAdv>100)
   {
     document.write("JEE-Main Cleared");
     if(jeeAdv>80)
     {
       document.write("<br/> JEE-Adv Cleared");
     }
     else
     {
       document.write("<br/> JEE-Main Cleared and JEE-Adv Not Cleared");
     }
   }
   else
   {
       document.write("Admission Rejected");
   }
   </script>
 </head>
 <body></body>
</html>

Output

JEE-Main Cleared
JEE-Adv Cleared

In the above code defines two constants, jeeMain and jeeAdv, that store the scores obtained by a student in JEE-Main and JEE-Advanced exams, respectively. The code then uses an if statement to check whether the student has cleared the JEE-Main exam with a score of more than 120 and the JEE-Advanced exam with a score of more than 100. If the student has cleared both exams, the code writes JEE-Main Cleared to the document using document.write(). The code then checks if the student has cleared the JEE-Advanced exam with a score of more than 80. If the student has cleared JEE-Advanced, the code writes JEE-Adv Cleared to the document on a new line using document.write(). If the student has not cleared JEE-Advanced, the code writes JEE-Main Cleared and JEE-Adv Not Cleared to the document on a new line using document.write(). If the student has not cleared JEE-Main or JEE-Advanced , the code writes Admission Rejected to the document using document.write().