Control Flow in JavaScript
Using if, else, and switch Statements

Understanding Control Flow in JavaScript

Control flow in JavaScript determines the direction in which the code executes. By default, JavaScript runs code from top to bottom, but using control structures like if, else, and switch, we can change this flow based on certain conditions.

if Statement

The if statement evaluates a condition. If it's true, it runs the associated block of code.

let age = 20;

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

Output:

You are eligible to vote.

Q: What happens if the condition is false?

A: Nothing inside the if block runs. Control moves to the next statement.

if...else Statement

Use else to define an alternative block that runs if the condition is false.

let temperature = 10;

if (temperature > 20) {
  console.log("It's warm outside.");
} else {
  console.log("It's cold outside.");
}
    

Output:

It's cold outside.

else if Ladder

Use else if to check multiple conditions in sequence. The first true condition will execute, and others will be skipped.

let score = 75;

if (score >= 90) {
  console.log("Grade: A");
} else if (score >= 80) {
  console.log("Grade: B");
} else if (score >= 70) {
  console.log("Grade: C");
} else {
  console.log("Grade: F");
}
    

Output:

Grade: C

Q: What if more than one condition is true?

A: Only the first true condition is executed. Others are ignored.

switch Statement

The switch statement is used when you want to compare one value against multiple possible matches.

let fruit = "apple";

switch (fruit) {
  case "banana":
    console.log("You chose banana.");
    break;
  case "apple":
    console.log("You chose apple.");
    break;
  case "mango":
    console.log("You chose mango.");
    break;
  default:
    console.log("Unknown fruit.");
}
    

Output:

You chose apple.

Why Use break in switch?

If you don't use break, JavaScript continues to execute the next cases even if a match is found (this is called “fall-through”).

let day = "Monday";

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

Output:

Start of the week
Second day

Tip: Always use break unless you intentionally want fall-through behavior.

Conclusion

• Use if and else if for range or boolean conditions.
• Use switch for fixed values comparison (e.g., exact matches).
• Never forget break in switch unless you need multiple cases to execute.