Conditional statements in JavaScript are used to execute different blocks of code based on certain conditions. They allow your program to make decisions and perform different actions depending on whether a condition evaluates to true or false.

Types of Conditional Statements

1. if Statement

   The if statement evaluates a condition and executes a block of code if the condition is true.

   if (condition) {
     // Code to execute if condition is true
   }
   

   Example:

   let number = 10;
   if (number > 5) {
     console.log('Number is greater than 5');
   }
   

   • Here, the message is logged only if number is greater than 5.

2. if...else Statement

   The if...else statement allows you to execute one block of code if the condition is true and another block if the condition is false.

   if (condition) {
     // Code to execute if condition is true
   } else {
     // Code to execute if condition is false
   }
   

   Example:

   let number = 4;
   if (number % 2 === 0) {
     console.log('Number is even');
   } else {
     console.log('Number is odd');
   }
   

   • The code checks if number is even or odd and logs the appropriate message.

3. if...else if...else Statement

   The if...else if...else statement allows you to test multiple conditions in sequence.

   if (condition1) {
     // Code to execute if condition1 is true
   } else if (condition2) {
     // Code to execute if condition2 is true
   } else {
     // Code to execute if none of the above conditions are true
   }
   

   Example:

   let score = 85;
   if (score >= 90) {
     console.log('Grade: A');
   } else if (score >= 80) {
     console.log('Grade: B');
   } else if (score >= 70) {
     console.log('Grade: C');
   } else {
     console.log('Grade: D');
   }
   

   • This example categorizes the score into different grades.

4. switch Statement

   The switch statement allows you to test a variable or expression against multiple values. It is often used when you have multiple possible values for a single variable.

   switch (expression) {
     case value1:
       // Code to execute if expression equals value1
       break;
     case value2:
       // Code to execute if expression equals value2
       break;
     // more cases...
     default:
       // Code to execute if no case matches
   }
   

   Example:

   let day = 3;
   switch (day) {
     case 1:
       console.log('Monday');
       break;
     case 2:
       console.log('Tuesday');
       break;
     case 3:
       console.log('Wednesday');
       break;
     default:
       console.log('Unknown day');
   }
   

   • The code prints the name of the day based on the value of day.

5. Ternary Operator

   The ternary operator is a shorthand way to write simple if...else statements. It takes three operands: a condition, a result for true, and a result for false.

   condition ? resultIfTrue : resultIfFalse;
   

   Example:

   let age = 18;
   let canVote = age >= 18 ? 'Yes' : 'No';
   console.log(canVote); // 'Yes'
   

   • This example checks if the age is 18 or older and assigns 'Yes' or 'No' to canVote based on the condition.

Key Points

• if Statements: Evaluate a condition and execute code based on whether the condition is true or false.
• if...else Statements: Provide two blocks of code to execute based on a condition.
• if...else if...else Statements: Handle multiple conditions in sequence.
• switch Statement: Test a variable or expression against multiple values and execute code based on the match.
• Ternary Operator: Provides a concise way to write simple conditional expressions.