JavaScript if….else Statement

By | February 8, 2021
JavaScript if....else Statement

During writing a program we often encounter situations where we want to execute a specific block of code only if a certain condition meets, else we want to execute another block of code. Let’s say you want to if a person’s age is between 20 and 23 then only he/she will be able to fill the form.

This kind of situation where the execution of code block depends upon the condition can be built using if…..else statements in the JavaScript.

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JavaScript Conditional Statement if….else Flow Chart

The if….else statement in JavaScript follows a Flow Control.

In JavaScript, we can create conditional statements using 3 statements

  • JavaScript if statement 
  • JavaScript if….else statement 
  • JavaScript if….else if…. statement 

JavaScript Conditional Statement: if statement

The JavaScript if statement is used when we want to execute a block of code only if a certain condition is true.

The JavaScript if  statement contains a conditional expression. And the conditional expression must be a boolean value or return a boolean value, and if the boolean value is true then only the block of code below the if statement, inside the curly brackets will execute.

JavaScript if statement Syntax

if (Conditional Expression)
    {
       //If Statement code block
    }

If the Conditional Expression value is false the browser will pass the if code block and will not execute it.

JavaScript if statement Example

The below example show the use case of the if statement.

<!DOCTYPE html>
<html>
    <head>
        <title></title>
        <script>
            document.write("<h1> JavaScript If example</h1>");
            let age = 21;
            if (age>=18)
            {
                document.write(" you are eligible to vote");
            }       
        </script>
    <body>       
    </body>
</html>

Output

JavaScript Conditional Statement: if…..else statement

Let’s say if the conditional statement is false and you want to execute another code of block which should execute only when the condition is false. Although you can also use the if statement with not operator to the conditional statement, but we should always use the else statement with the if statement to represent the code block for the false condition.

The else statement can not be implemented alone it needs to be a part of if statement.

JavaScript if…else statement Syntax

if (Conditional Expression)
    {
       //If Statement code block
    }
else
   {
     //else statement code block
   }

The else statement code block will only execute when the conditional expression is false.

JavaScript if…else statement Example

The below example demonstrates the use of JavaScript if…else statement.

<!DOCTYPE html>
<html>
    <head>
        <title></title>
        <script>
            document.write("<h3> JavaScript If...else example</h3>");
            let age = 17;

            if (age>=18) //false
            {
                document.write("You are eligible to vote");
            }       
            else
            {
                document.write("You are under Age to give vote")
            }
        </script>
    <body>       
    </body>
</html>

Output

JavaScript ternary operator

The JavaScript ternary operator is an alternative approach to write if….else statement in a single line.

The like a JavaScript if...else statement ternary statement works on 3 operands, condition, true value, and false value.

JavaScript ternary operator syntax

condition? true statement : false statement

JavaScript ternary operator Example

We can perform the above if....else statement with the JavaScript ternary operator within a single line.

<!DOCTYPE html>
<html>
    <head>
        <title></title>
        <script>
            document.write("<h3> JavaScript Ternary example</h3>");
            let age = 17;
            //JavaScript ternary operator
            document.write( (age>18)? "You are eligible to vote" :"You are under Age to give vote");
        </script>
    <body>       
    </body>
</html>

JavaScript Conditional Statement: if…..else if… statement

With simple JS if  statement we have a single block of code to execute on a single condition, with JS if....else statement we can execute one of the two-block of code based on one condition, but with JavaScript if...else if.... statement we can execute one of the code blocks based on multiple conditions.

The if....else if..... statement is an advancement of if...else statement, in this we can have multiple conditional expressions and only one of them will execute.

You can argue that why use if...else if.... statement when we can have multiple if statements that will work the same. The answer is simple the JavaScript will keep paring the multiple if statements even if one of them is true, but in the case of if.....elseif.. the JavaScript will only parse the statement until it finds the true condition if it finds the true condition in between it will not the further else if conditions.

JavaScript if…else statement Syntax

if (Conditional Expression1)
  {
     //If Statement code block
  }
else if (Conditional Expression2)
  {
     //else If Statement2 code block
  }
if (Conditional Expression 3)
  {
     //else If Statement3 code block
  }
if (Conditional Expression3)
  {
     //If Statement3 code block
  }
else
{
//else statement code block
}

Similar to the if..else statement the else if statement can not be implemented alone it needs to be a part of the if statement. And we can have an else statement, at last, that will execute if all the conditional expressions are false.

JavaScript if…else if……else Example

The below example show the real use case of JavaScript if…else if.. statement

<!DOCTYPE html>
<html>
    <head>
        <title></title>
        <script>
            document.write("<h3> JavaScript IF ELSE IF example</h3>");
            let marks =89;
            let grade;
            if(marks==100)
            {
                grade= "A++";
            }
            else if(marks >= 90 && marks <=99)
            {
                grade ="A";
            }
            else if(marks >=80 && marks <=89)
            {
                grade="B++";
            }
            else if (marks>=70 && marks<=79)
            {
                grade="B";
            }
            else
            {
                grade ="C"
            }
            document.write("Grades: "+ grade);
        </script>
    <body>       
    </body>
</html>

Output

Summary

  • The JavaScript if-else statement is used for conditional statements.
  • The if statement can be implemented alone.
  • The if statement takes the conditional expression, which must be or return a boolean value.
  • The if statement block will only execute if the conditional expression value is true.
  • The else statement will execute when the if conditional expression value is false.
  • The if-else-if statement is used to put multiple conditional statements.
  • The ternary operator is a shorthand alternative to write the if-else statement in a single line.

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