JavaScript Conditional Statements

You are reading Part 4 of the 39-part series: JavaScript Skill Progression: The Path from Beginner to Extreme. [Level 1]

Introduction

Conditional statements allow JavaScript to make decisions based on conditions. These conditions evaluate to true or false, enabling the execution of specific blocks of code accordingly. The most commonly used conditional statements in JavaScript are if, else if, else, and switch.

Conditional statements are essential in JavaScript for controlling the flow of execution based on different conditions. if, if-else, and switch statements help in making logical decisions within programs, allowing dynamic and responsive applications.

The if Statement

The if statement executes a block of code if a specified condition evaluates to true.

Syntax:

if (condition) {
    // Code to execute if condition is true
}

Example:

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

The if-else Statement

The if-else statement provides an alternative execution path if the initial condition evaluates to false.

Syntax:

if (condition) {
    // Code to execute if condition is true
} else {
    // Code to execute if condition is false
}

Example:

let age = 16;
if (age >= 18) {
    console.log("You are an adult.");
} else {
    console.log("You are a minor.");
}

The if-else if-else Statement

The if-else if-else statement allows multiple conditions to be checked in sequence. The first condition that evaluates to true determines which block of code runs.

Syntax:

if (condition1) {
    // Code to execute if condition1 is true
} else if (condition2) {
    // Code to execute if condition2 is true
} else {
    // Code to execute if none of the conditions are true
}

Example:

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");
}

The switch Statement

The switch statement is used when multiple conditions depend on the same expression. It provides a cleaner alternative to multiple if-else if statements.

Syntax:

switch (expression) {
    case value1:
        // Code to execute if expression === value1
        break;
    case value2:
        // Code to execute if expression === value2
        break;
    default:
        // Code to execute if no match is found
}

Example:

let day = "Monday";
switch (day) {
    case "Monday":
        console.log("Start of the workweek.");
        break;
    case "Friday":
        console.log("End of the workweek!");
        break;
    case "Saturday":
    case "Sunday":
        console.log("It’s the weekend!");
        break;
    default:
        console.log("Midweek day.");
}

Break and Default in Switch Statements

• break: Stops execution and exits the switch statement after a case is matched.

• default: Executes when no case matches the expression.

You are reading Part 4 of the 39-part series: JavaScript Skill Progression: The Path from Beginner to Extreme. [Level 1]