In JavaScript, conditional statements control the flow of code based on whether certain conditions are true or false. They allow the program to make decisions and execute different blocks of code depending on those conditions.

Here are the main types of conditional statements in JavaScript:

1. if Statement

The if statement executes a block of code if a specified condition is true.

let age = 18;
if (age >= 18) {
  console.log("You are an adult.");
}

2. if...else Statement

The if...else statement adds an alternative block of code to run if the condition is false.

let age = 16;
if (age >= 18) {
  console.log("You are an adult.");
} else {
  console.log("You are a minor.");
}

3. else if Statement

The else if statement lets you specify multiple conditions to check in sequence. If the first condition is false, it moves to the next else if condition.

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

4. switch Statement

The switch statement allows for multiple possible code blocks to run based on the value of an expression. It’s often used as a cleaner alternative to multiple if...else if statements.

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("Other day");
}

5. Ternary Operator (? :)