JavaScript Control Statements

What Are Control Statements?

Control statements allow your JavaScript code to make decisions. They let you run specific blocks of code based on certain conditions.

In short:
“If this is true, do that. Otherwise, do something else.”

if, else if, else

The if statement is used to test a condition. If it evaluates to true, the block of code inside runs.

Basic if Statement:

let score = 85;

if (score >= 80) {
  console.log("Excellent!");
}

if…else Statement:

let score = 65;

if (score >= 80) {
  console.log("Excellent!");
} else {
  console.log("Keep practicing.");
}

if…else if…else:

When you want to test multiple conditions, use else if.

let score = 70;

if (score >= 90) {
  console.log("Outstanding");
} else if (score >= 75) {
  console.log("Very Good");
} else if (score >= 60) {
  console.log("Good");
} else {
  console.log("Needs Improvement");
}

if…else Ladder

This is just a fancy name for chaining multiple else if conditions as seen above.

Use it when you have several distinct conditions to check one after another.

Example:

let day = 2;

if (day === 1) {
  console.log("Monday");
} else if (day === 2) {
  console.log("Tuesday");
} else if (day === 3) {
  console.log("Wednesday");
} else {
  console.log("Another day");
}

switch Case

The switch statement is another way to check multiple conditions, especially when you’re comparing the same variable against different values.

Syntax:

switch (expression) {
  case value1:
    // code
    break;
  case value2:
    // code
    break;
  default:
    // fallback code
}

Example:

let fruit = "apple";

switch (fruit) {
  case "banana":
    console.log("Banana is yellow.");
    break;
  case "apple":
    console.log("Apple is red.");
    break;
  case "grape":
    console.log("Grape is purple.");
    break;
  default:
    console.log("Unknown fruit.");
}

Important Note:
Use break after each case to prevent fall-through (accidentally running multiple cases).

Ternary Operator Examples

The ternary operator is a shorthand way to write an if...else statement in a single line.

Syntax:

condition ? expressionIfTrue : expressionIfFalse;

Example 1: Basic Usage

let age = 20;
let message = age >= 18 ? "Adult" : "Minor";
console.log(message); // "Adult"

Example 2: Nested Ternary

let marks = 85;

let grade = marks >= 90
  ? "A"
  : marks >= 80
  ? "B"
  : marks >= 70
  ? "C"
  : "D";

console.log(grade); // "B"

Note:
Ternary operators are great for simple conditions, but avoid nesting too deeply—use if...else if clarity is more important.

Summary

• Use if, else if, and else to make decisions in your code.
• Use if...else ladder when checking many related conditions.
• Use switch for comparing one variable to multiple fixed values.
• Use the ternary operator for short, clean one-line conditionals.