JavaScript Control Structures: If Statements and Conditionals

Making Decisions with Conditional Statements

Conditional statements allow your program to make decisions and execute different code based on different conditions.

The if Statement

let age = 18;

if (age >= 18) {
    console.log("You are an adult!");
}

The if...else Statement

let temperature = 25;

if (temperature > 30) {
    console.log("It's hot outside!");
} else {
    console.log("It's not too hot.");
}

The if...else if...else Statement

let score = 85;

if (score >= 90) {
    console.log("Grade: A");
} else if (score >= 80) {
    console.log("Grade: B");
} else if (score >= 70) {
    console.log("Grade: C");
} else if (score >= 60) {
    console.log("Grade: D");
} else {
    console.log("Grade: F");
}

Logical Operators in Conditions

let age = 25;
let hasJob = true;
let income = 50000;

// AND operator
if (age >= 18 && hasJob) {
    console.log("Eligible for credit card");
}

// OR operator
if (age >= 65 || income < 20000) {
    console.log("Eligible for discount");
}

// NOT operator
if (!hasJob) {
    console.log("Looking for employment");
}

Nested if Statements

let weather = "sunny";
let temperature = 22;

if (weather === "sunny") {
    if (temperature > 20) {
        console.log("Perfect day for a picnic!");
    } else {
        console.log("Sunny but a bit cold.");
    }
} else {
    console.log("Maybe stay indoors.");
}

The switch Statement

let dayOfWeek = 3;
let dayName;

switch (dayOfWeek) {
    case 1:
        dayName = "Monday";
        break;
    case 2:
        dayName = "Tuesday";
        break;
    case 3:
        dayName = "Wednesday";
        break;
    case 4:
        dayName = "Thursday";
        break;
    case 5:
        dayName = "Friday";
        break;
    case 6:
        dayName = "Saturday";
        break;
    case 7:
        dayName = "Sunday";
        break;
    default:
        dayName = "Invalid day";
}

console.log(dayName);  // "Wednesday"

Ternary Operator (Conditional Operator)

let age = 20;
let status = age >= 18 ? "adult" : "minor";
console.log(status);  // "adult"

// Multiple ternary operators
let score = 85;
let grade = score >= 90 ? "A" : score >= 80 ? "B" : score >= 70 ? "C" : "F";
console.log(grade);  // "B"

Practice Exercise: Simple Calculator

let num1 = 10;
let num2 = 5;
let operation = "+";

if (operation === "+") {
    console.log(`${num1} + ${num2} = ${num1 + num2}`);
} else if (operation === "-") {
    console.log(`${num1} - ${num2} = ${num1 - num2}`);
} else if (operation === "*") {
    console.log(`${num1} * ${num2} = ${num1 * num2}`);
} else if (operation === "/") {
    if (num2 !== 0) {
        console.log(`${num1} / ${num2} = ${num1 / num2}`);
    } else {
        console.log("Error: Division by zero!");
    }
} else {
    console.log("Invalid operation!");
}

// Age category checker
let userAge = 25;
let category;

if (userAge < 13) {
    category = "child";
} else if (userAge < 20) {
    category = "teenager";
} else if (userAge < 60) {
    category = "adult";
} else {
    category = "senior";
}

console.log(`Age category: ${category}`);