JavaScript Control Statements – Conditional Statements

Here, we will learn Control statements – conditional statements in JavaScript.

Control Statements decide according to the condition whether a statement should be executed or not. In this post, we further go into detail about these control statements.

This post is to give a basic introduction to control statements in Javascript. At the end of this article, you will clearly understand the usage of conditional statements.

Types of Control Statements in JavaScript

  1. Conditional statements
  2. Loop /Iterative Statements

Let’s understand them with the examples:

  1. Conditional Statements: if,  if-else,  else-if ladder,  switch

IF Statement

The syntax for if statement in JavaScript.

if(condition){
//block of code 
}

example:

<html lang="en">
<head>
 <title>if statement</title>
 <script language="javascript" type="text/javascript" >
 var a = window.prompt("Enter a number", "0");
 a = parseInt(a);
 if(a<100){
 document.writeln("The number is less than 100");
 }
 </script> 
</head>
<body>
</html>

IF-ELSE Statement

The syntax for the if-else statement in JavaScript.

if(condition){
//block of code 
}else{
//block of code 
}

example:

<!doctype html>
<html lang="en">
<head>
 <title>if-else statement</title>
 <script language="javascript" type="text/javascript" >
 var a = window.prompt("Enter a number", "0");
 a = parseInt(a);
 var b= parseInt(prompt("Enter b number"));
 if(a > b)
 window.alert("The greatest is " +a);
 else 
 alert("The greatest is " +b); 
 
 </script> 
</head>
<body>
</html>

ELSE-IF Statement

The syntax for the else-if statement in JavaScript.

if(condition1){
//logic 
}else if(condition2){
//logic
}else{
//logic
}

example:

<!-- Arranging 3 numbers in order -->
<!doctype html>
<html lang="en">
<head>
 <title>nested if statement</title>
</head>
<body>
 <script language="javascript" type="text/javascript" >
 var a = parseInt(window.prompt("Enter Marks Sub1"));
 var b= parseInt(prompt("Enter Marks Sub2"));
 var c= parseInt(prompt("Enter Marks Sub3"));
 var avg=(a+b+c)/3;
 if(avg >= 70)
    alert("First With Distinction");
 else if(avg >=60 && avg <70)
    alert("First Class");
 else if(avg >=50 && avg <60)
    alert("Second Class");
 else if(avg >=40 && avg <50)
    alert("Third Class");
 else
    alert("Fail"); 
 </script> 
</body>
</html

SWITCH Statement

The syntax for the switch statement in JavaScript.

switch(expression) {
  case x:
    // block of code 
    break;
  case y:
    // block of code 
    break;
  default:
    // default block 
}

example:

<!-- finding the grade using switch -->
<html>
 <head> 
 <title> switch </title>
 </head>
 <script language="javascript" type="text/javascript">
 
 var n1 = parseInt(window.prompt("Enter the marks in Sub1"));
 var n2 = parseInt(window.prompt("Enter the marks in Sub2"));
 var n3 = parseInt(window.prompt("Enter the marks in Sub3"));
 var avg= (n1+n2+n3)/3;
 
 var ch = parseInt(avg/10); //parse to int
 
 switch(ch)
 {
 case 10:
 case 9:
 case 8:
 case 7: window.alert("Distinction");break;
 case 6: window.alert("First Class");break;
 case 5: window.alert("Second Class");break;
 case 4: window.alert("Third Class ");break;
 default: window.alert("Fail ");
 }
 </script>
 </body>
</html>

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