When we write programs, the computer must make decisions.

Just like humans make decisions every day.

Example in real life:

• If it is raining → take an umbrella

• If you are hungry → eat food

• If the traffic light is red → stop

Programming works the same way.
The computer checks a condition, then decides what code should run.

This idea is called Control Flow.

Control flow simply means:

Controlling which part of the program runs depending on conditions.

In JavaScript, the main control flow tools are:

• if

• if-else

• else if

• switch

Let’s understand them step by step.

---

1. The if Statement

The if statement runs code only if a condition is true.

Example

Suppose we check if someone is 18 or older.

let age = 20;

if (age >= 18) {
  console.log("You can vote");
}

How the code runs

Step 1
Check condition:

age >= 18

Step 2
If the condition is true, the code inside {} runs.

Output:

You can vote

If the condition is false, nothing happens.

---

2. The if-else Statement

Sometimes we want two possibilities.

Example:

• If you pass → celebrate

• Else → study more

Example

let marks = 40;

if (marks >= 35) {
  console.log("You passed");
} else {
  console.log("You failed");
}

Step-by-step

1️⃣ Check condition

marks >= 35

2️⃣ If true → run if block

3️⃣ If false → run else block

Output:

You passed

---

3. The else if Ladder

Sometimes there are many possibilities.

Example:

Student grades.

• 90+ → A grade

• 75+ → B grade

• 50+ → C grade

• below 50 → Fail

Example

let marks = 82;

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

How it runs

JavaScript checks conditions one by one from top to bottom.

First true condition will run.

Output:

Grade B

Because 82 >= 75.

---

Simple Visualization of if-else

Check condition
      |
   true?
   /   \
 yes    no
  |      |
run if  run else

---

4. The switch Statement

When we compare one value with many options, switch can be cleaner.

Example: Days of the week

Example

let day = 3;

switch(day) {

  case 1:
    console.log("Monday");
    break;

  case 2:
    console.log("Tuesday");
    break;

  case 3:
    console.log("Wednesday");
    break;

  case 4:
    console.log("Thursday");
    break;

  case 5:
    console.log("Friday");
    break;

  default:
    console.log("Weekend");
}

Output:

Wednesday

Because day = 3.

---

Why break is Important

Inside switch, break stops the execution.

Without break, JavaScript keeps running the next cases.

Example without break:

Wednesday
Thursday
Friday

That is why break is very important.

---

Simple Visualization of Switch

        value
          |
      switch(value)
       /   |   \
   case1 case2 case3
     |      |      |
    run    run    run

The case that matches the value will execute.

---

When to Use switch vs if-else

Use if-else when:

• Checking ranges

• Complex conditions

Example:

marks > 75
age >= 18
temperature > 30

Use switch when:

• Checking one variable

• Comparing fixed values

Example:

day of week
menu selection
user role

Example comparison:

Using if-else

if(day === 1){
 console.log("Monday");
}

Using switch

switch(day){
 case 1:
 console.log("Monday");
}

switch becomes cleaner when there are many values.

---

Assignment Practice

Try these programs in your browser console.

---

1. Check Positive, Negative, or Zero

let num = -5;

if (num > 0) {
  console.log("Positive number");
} 
else if (num < 0) {
  console.log("Negative number");
} 
else {
  console.log("Zero");
}

Example outputs:

Positive number

or

Negative number

or

Zero

Why we used if-else

Because we are checking conditions and ranges.

---

2. Print Day of the Week using Switch

let day = 2;

switch(day){

  case 1:
    console.log("Monday");
    break;

  case 2:
    console.log("Tuesday");
    break;

  case 3:
    console.log("Wednesday");
    break;

  case 4:
    console.log("Thursday");
    break;

  case 5:
    console.log("Friday");
    break;

  case 6:
    console.log("Saturday");
    break;

  case 7:
    console.log("Sunday");
    break;

  default:
    console.log("Invalid day");
}

Output:

Tuesday

Why we used switch

Because we are comparing one variable (day) with many fixed values.

---

Final Thoughts

Control flow is one of the most important concepts in programming.

It allows programs to make decisions just like humans do.

The most important tools are:

• if

• if-else

• else if

• switch

Once you understand these, you can build real-world applications like:

• login systems

• form validation

• role-based dashboards

• games and apps

Best way to learn?

Open your browser console and try the examples yourself.

Happy coding 🚀