Control flow statements are used in JavaScript to control the order of execution of statements in a program based on certain conditions. The three main types of control flow statements in JavaScript are if/else statements, switch/case statements, and loops.

1. If/else statements:

If/else statements are used to execute different blocks of code based on whether a certain condition is true or false.

Syntax:

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

Example program:

let x = 5;

if (x > 2) {
  console.log("x is greater than 2");
} else {
  console.log("x is less than or equal to 2");
}

Output: “x is greater than 2”

2. Switch/case statements:

Switch/case statements are used to select one of many blocks of code to execute based on the value of a given expression.

Syntax:

switch (expression) {
  case value1:
    // code to execute if expression equals value1
    break;
  case value2:
    // code to execute if expression equals value2
    break;
  default:
    // code to execute if expression doesn't match any of the cases
}

Example program:

let day = "Monday";

switch (day) {
  case "Monday":
    console.log("Today is Monday");
    break;
  case "Tuesday":
    console.log("Today is Tuesday");
    break;
  default:
    console.log("Today is neither Monday nor Tuesday");
}

Output: “Today is Monday”

3. Loops:

Loops are used to repeat a block of code multiple times.

a. For loop:

For loop is used when you know how many times you need to execute a block of code.

Syntax:

for (initialization; condition; increment/decrement) {
  // code to execute in each iteration
}

Example program:

for (let i = 1; i <= 5; i++) {
  console.log(i);
}

Output:

1 2 3 4 5

b. While loop:

While loop is used when you don’t know how many times you need to execute a block of code, but you know the condition that must be met for the loop to continue.

Syntax:

while (condition) {
  // code to execute in each iteration
}

Example program:

let i = 1;

while (i <= 5) {
  console.log(i);
  i++;
}

Output:

1 2 3 4 5

c. Do/while loop:

Do/while loop is similar to a while loop, but it executes the block of code at least once, even if the condition is false.

Syntax:

do {
  // code to execute in each iteration
} while (condition);

Example program:

let i = 1;

do {
  console.log(i);
  i++;
} while (i <= 5);

Output:

1 2 3 4 5

Control flow statements are essential for controlling the order of execution of statements in a program. By understanding these statements, you can write more complex programs that make decisions and repeat actions based on certain conditions.