Control Flow in JavaScript: If, Else, and Switch Explained

When writing programs, we often need the code to make decisions. Sometimes the program should do one thing, and sometimes it should do something else depending on a condition. This concept is called control flow.

In simple terms, control flow decides which part of the code runs and when.

Think of it like real-life decision making.

For example:

• If it is raining → take an umbrella

• If your exam score is above 50 → you pass

• If it is Sunday → relax

Programming works in a similar way. JavaScript provides several control structures to handle these situations.

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What is Control Flow in Programming?

Control flow refers to the order in which statements in a program are executed.

Normally, code runs from top to bottom. But with control flow statements, we can change that order based on conditions.

For example:

let age = 20;

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

Here the message only prints if the condition is true.

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The if Statement

The if statement is the simplest decision-making structure in JavaScript.

It checks a condition and runs a block of code only if that condition is true.

Syntax

if (condition) {
  // code runs if condition is true
}

Example

let marks = 75;

if (marks >= 50) {
  console.log("You passed the exam.");
}

If the marks are 50 or more, the message will appear.

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The if-else Statement

Sometimes we want one action when a condition is true and another when it is false. That’s where if-else comes in.

Syntax

if (condition) {
  // code if true
} else {
  // code if false
}

Example

let age = 16;

if (age >= 18) {
  console.log("You can vote.");
} else {
  console.log("You are too young to vote.");
}

Only one block runs depending on the condition.

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Diagram: If-Else Decision Flow

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The else if Ladder

When there are multiple conditions, we use else if.

This allows the program to check conditions one by one until one of them is true.

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");
}

The program checks conditions from top to bottom.

Once a condition is true, the rest are skipped.

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The switch Statement

The switch statement is used when we want to compare one value with many possible cases.

It often looks cleaner than multiple if-else statements.

Syntax

switch (expression) {
  case value1:
    // code
    break;

  case value2:
    // code
    break;

  default:
    // runs if no case matches
}

Example: Day of the Week

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;

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

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

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

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Diagram: Switch Case Flow

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Why break is Important in Switch

The break statement stops the execution of the switch once a match is found.

Without break, JavaScript will continue running the next cases.

Example without break:

let day = 1;

switch (day) {
  case 1:
    console.log("Monday");
  case 2:
    console.log("Tuesday");
}

Output:

Monday
Tuesday

This happens because execution falls through to the next case.

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When to Use switch vs if-else

Situation	Best Choice
Checking ranges (marks, age etc.)	if-else
Comparing one value with many options	switch
Complex logical conditions	if-else
Simple value matching	switch

Example:

Checking grades → if-else

Checking day number → switch

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Assignment Practice Examples

• Check if a Number is Positive, Negative, or Zero

let number = -5;

if (number > 0) {
  console.log("Positive number");
} else if (number < 0) {
  console.log("Negative number");
} else {
  console.log("The number is zero");
}

We use if-else here because we are checking different ranges of values.

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• Print the Day of the Week Using Switch

let day = 5;

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("Invalid day");
}

Here switch is useful because we are matching one value with multiple fixed options.