JavaScript if, else if, else Statements

JavaScript if-else Statements

In JavaScript, conditional statements are used to control the flow of the program. The most common conditional statements are if, else, and else if.

These statements help you execute certain blocks of code based on whether a condition evaluates to true or false.

Types of if-else Statements

  • if statement
  • if-else statement
  • else-if statement

1. if Statement

You use the if statement to execute a block of code if a given condition evaluates to true.

   if (condition) {
    // code to be executed if condition is true
    }

Example: Simple if Statement

    if (5 > 3) {
    alert("5 is greater than 3");
    }

    if (2 < 1) {
    alert("2 is less than 1");
    }

In this example, the first if condition 5 > 3 evaluates to true, so the alert box "5 is greater than 3" will show up. The second condition 2 < 1 is false, so no alert will appear.

Using Variables in if Conditions

    var age = 25;
    var minimumAge = 18;

    if (age >= minimumAge) {
    alert("You are eligible to vote!");
    }

This example compares two variables to check if someone is old enough to vote. If the condition evaluates to true, an alert message will be shown.

Curly Braces

If the if block contains only one statement, you can skip the curly braces {}.

    if (10 === 10) alert("10 equals 10");

Comparison Operators

Be careful when using comparison operators like == and ===. The == operator checks only for equality in value, while === checks both value and type.

    if (2 == "2") {
    alert("== operator does not consider types of operands");
    }

    if (2 === "2") {
    alert("=== operator considers types of operands");
    }

2. else Statement

The else statement is used when you want to execute a block of code when the if condition evaluates to false.

    if (condition) {
    // Execute this code if true
    } else {
    // Execute this code if false
    }

Example: Simple if-else Statement

    var temperature = 15;

    if (temperature > 20) {
    alert("It's warm outside");
    } else {
    alert("It's cold outside");
    }

3. else if Statement

You can use else if to test multiple conditions after an if statement. If the if condition is false, it checks the else if condition.

    if (condition) {
    // Execute this code if true
    } else if (condition) {
    // Execute this code if this second condition is true
    }

Example: Using else if

    var day = "Monday";

    if (day === "Friday") {
    alert("It's almost the weekend!");
    } else if (day === "Monday") {
    alert("The week just started!");
    } else {
    alert("It's a regular day.");
    }

Multiple else if Statements

You can use multiple else if statements to check several conditions one after the other.

    var score = 85;

    if (score >= 90) {
    alert("You got an A");
    } else if (score >= 80) {
    alert("You got a B");
    } else if (score >= 70) {
    alert("You got a C");
    } else {
    alert("You failed");
    }

Points to Remember

  • Use if-else statements to control the flow of the program based on conditions.
  • There are three main types: if condition, if-else condition, and else-if condition.
  • The if condition must have a conditional expression inside parentheses (), followed by either a single statement or a code block wrapped in curly braces {}.
  • The else if statement must come after an if condition, and can be used multiple times.
  • There must be only one else statement at the end, and it comes after all if or else if statements.
Note: The else statement is optional. If it's not provided, no code will be executed when the condition is false.