In programming, we often need our code to make decisions.

For example:

• If a user is 18 or older, allow them to register.

• If a student scores above 90, assign grade A.

• If a user selects a menu option, perform a specific action.

Just like in real life, programs also need to choose between different paths. This concept is called control flow.

In this article, we’ll learn the most common decision-making tools in JavaScript:

• if statement

• if...else statement

• else if ladder

• switch statement

• When to use switch vs if-else

All examples are kept simple and beginner-friendly, so you can try them in your browser console or Node.js.

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What is Control Flow?

Control flow refers to the order in which the program executes instructions.

Normally, code runs from top to bottom.

Example:

console.log("Start");
console.log("Learning JavaScript");
console.log("End");

Output:

Start
Learning JavaScript
End

But sometimes we want the program to run certain code only if a condition is true. That’s where control flow statements like if and switch come in.

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The if Statement

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

Syntax

if (condition) {
  // code to run if condition is true
}

Example: Checking Age

let age = 20;

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

Step-by-step execution

1. JavaScript checks the condition → age >= 18

2. 20 >= 18 is true

3. The code inside the if block runs.

Output:

You are eligible to vote.

If the condition were false, nothing would run.

---

The if...else Statement

Sometimes we want two possible outcomes.

For example:

• If a person is 18 or older → allow access

• Otherwise → deny access

Syntax

if (condition) {
  // runs if condition is true
} else {
  // runs if condition is false
}

Example

let age = 16;

if (age >= 18) {
  console.log("You can vote.");
} else {
  console.log("You cannot vote yet.");
}

Step-by-step execution

1. Check condition → 16 >= 18

2. Condition is false

3. JavaScript runs the else block

Output:

You cannot vote yet.

---

The else if Ladder

Sometimes there are multiple conditions to check.

Example: Assigning grades based on marks.

Example

let marks = 85;

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");
}

Step-by-step execution

JavaScript checks conditions from top to bottom:

1. 85 >= 90 → false

2. 85 >= 75 → true

Once a condition becomes true, the remaining conditions are not checked.

Output:

Grade B

---

The switch Statement

The switch statement is another way to make decisions when we have multiple possible values for the same variable.

Syntax

switch (value) {
  case option1:
    // code
    break;

  case option2:
    // code
    break;

  default:
    // code
}

---

Example: Menu Selection

let day = "Monday";

switch (day) {
  case "Monday":
    console.log("Start of the work week");
    break;

  case "Friday":
    console.log("Almost weekend");
    break;

  case "Sunday":
    console.log("Weekend!");
    break;

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

Output:

Start of the work week

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Why break is Important in switch

The break statement stops the switch block after a match is found.

Without break, JavaScript will continue executing the next cases.

Example without break:

let number = 1;

switch (number) {
  case 1:
    console.log("One");
  case 2:
    console.log("Two");
}

Output:

One
Two

This happens because there is no break after case 1.

Correct version:

switch (number) {
  case 1:
    console.log("One");
    break;

  case 2:
    console.log("Two");
    break;
}

Output:

One

So always remember:
break prevents execution from continuing into other cases.

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When to Use switch vs if-else

Use if-else when:

• Conditions involve ranges

• Conditions involve different variables

• Logical operators are used (&&, ||)

Example:

if (marks > 90)

---

Use switch when:

• Checking one variable

• Comparing specific values

• Multiple possible options exist

Example:

switch(day)

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Example Comparison

Using if-else:

if (day === "Monday") {
  console.log("Start of week");
}

Using switch:

switch (day) {
  case "Monday":
    console.log("Start of week");
    break;
}

Both work, but switch is often cleaner when there are many options.

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Control flow allows your program to make decisions and behave differently depending on conditions.

The most commonly used tools are:

• if → run code if a condition is true

• if...else → choose between two outcomes

• else if → check multiple conditions

• switch → handle multiple possible values