JavaScript if-else with examples

Introduction

• The if-else statement in JavaScript executes a certain code block based on a certain condition.
• When the condition is evaluated as true, the code block inside the if statement is executed.
• If the condition is false, the else block runs instead.

Note: The if statement can be used without an else statement if no action is needed when the condition is false.

Syntax:

if(condition){
    //Executes when condition is true
}else{
   //Executes when condition is false
}

1. simple(if) statement

To check one condition and execute code when it’s true, you can use a standalone if statement.

Example:

let temp = 31;
if(temp>30){
   console.log("It's a sunny day.");
}

This code will output the statement ‘It’s a sunny day.’ when the temperature is higher than 30.

Output: 

It's a sunny day.

2. if-else statement

An else statement can follow an if statement to execute code when the if condition is false.

Example:

let cadage = 20;
if(cadage>=18){
   console.log("Valid Age");
}else{
   console.log("Invalid Age");
}

Output:

Valid Age

As the age of the candidate is 20 which is greater than 18. So he/she is eligible to apply for a particular job.

3. else-if statement

let precentage = 85;

if (precentage >= 90) {
    console.log("Grade: A");
} else if (precentage >= 75) {
    console.log("Grade: B");
} else if (precentage >= 50) {
    console.log("Grade: C");
} else {
    console.log("Grade: F");
}

Output:

Grade: B

As the percentage is 85 which is smaller than 90 and greater than 75. So the grade is B.

4. Nested if-else statement

To check on multiple conditions nesting of if-else is used.

Example:

let num = 5;
let result;

if(num > 0){
   if(num%2 === 0){
      result = "Positive even number";
   }else{
      result = "Positive odd number";
   }
}else{
if (num < 0){
   result = "Negative number";
}else{
   result = "The number is zero";
   }
}
console.log(result);

Output:

Positive odd number

Summary:

• Use if when you have a single condition to check.
• Use if-else for two possible outcomes.
• Use else-if for multiple conditions.
• Use nested if-else statements for more complex conditions.